/*
 * Electronics From Zero: shared stylesheet.
 * Layout: graph-paper page; site header, then one reading column (with a sticky
 * chapter rail on the course page). Interactive work sits on "bench" panels
 * with live schematics and LCD-style meters.
 * Every colour is a token defined for light and dark themes below.
 */
:root{
  --paper:#EDF2EE; --panel:#FBFDFB; --ink:#13261F; --muted:#4D6157; --line:#CCD9D0; --grid:rgba(19,38,31,.055);
  --copper:#AF5418; --copper-soft:rgba(175,84,24,.11); --on-copper:#FFFFFF;
  --signal:#1C5BC9; --live:#C42F2A; --ok:#1B7A49; --glow:#FFB31F; --lo:#9DAEA5;
  --lcd-bg:#D8E3CA; --lcd-fg:#1B2911;
  --scope-bg:#0E1A16; --scope-grid:rgba(190,230,210,.13); --scope-trace:#FFC94D; --scope-text:#A9C4B7;
  --resistor-body:#D9BE8A;
  --caution:#8F5B00; --violet:#6B4FC8; --ok-soft:rgba(27,122,73,.12); --caution-soft:rgba(176,112,0,.13); --danger-soft:rgba(196,47,42,.11); --code-bg:#E3EAE5;
  --f-display:"Chakra Petch","Segoe UI",system-ui,sans-serif;
  --f-body:"Atkinson Hyperlegible",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  --f-mono:"JetBrains Mono",ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){
    --paper:#0C1512; --panel:#121F1A; --ink:#E1EBE5; --muted:#93A79D; --line:#24362E; --grid:rgba(225,235,229,.045);
    --copper:#E28A4D; --copper-soft:rgba(226,138,77,.13); --on-copper:#1B0D03;
    --signal:#76A6FF; --live:#FF7468; --ok:#55C890; --glow:#FFC24D; --lo:#4B5E55;
    --lcd-bg:#1A2A1E; --lcd-fg:#BFE6A1;
    --scope-bg:#08110E; --scope-grid:rgba(190,230,210,.11); --scope-trace:#FFC94D; --scope-text:#8FAA9D;
    --resistor-body:#C9AC77;
    --caution:#F2B54A; --violet:#A893FF; --ok-soft:rgba(85,200,144,.13); --caution-soft:rgba(242,181,74,.13); --danger-soft:rgba(255,116,104,.13); --code-bg:#16251F;
    color-scheme:dark;
  }
}
:root[data-theme="dark"]{
  --paper:#0C1512; --panel:#121F1A; --ink:#E1EBE5; --muted:#93A79D; --line:#24362E; --grid:rgba(225,235,229,.045);
  --copper:#E28A4D; --copper-soft:rgba(226,138,77,.13); --on-copper:#1B0D03;
  --signal:#76A6FF; --live:#FF7468; --ok:#55C890; --glow:#FFC24D; --lo:#4B5E55;
  --lcd-bg:#1A2A1E; --lcd-fg:#BFE6A1;
  --scope-bg:#08110E; --scope-grid:rgba(190,230,210,.11); --scope-trace:#FFC94D; --scope-text:#8FAA9D;
  --resistor-body:#C9AC77;
  --caution:#F2B54A; --violet:#A893FF; --ok-soft:rgba(85,200,144,.13); --caution-soft:rgba(242,181,74,.13); --danger-soft:rgba(255,116,104,.13); --code-bg:#16251F;
  color-scheme:dark;
}
*{box-sizing:border-box}
[hidden]{display:none!important}
:root{color-scheme:light}
body{margin:0}
img,svg,canvas{max-width:100%}
[hidden]{display:none!important}
html{scroll-behavior:smooth;scroll-padding-top:calc(env(safe-area-inset-top,0px) + 72px)}
@media (prefers-reduced-motion: reduce){html{scroll-behavior:auto}}
body{
  background-color:var(--paper);
  background-image:linear-gradient(var(--grid) 1px,transparent 1px),linear-gradient(90deg,var(--grid) 1px,transparent 1px);
  background-size:24px 24px;
  color:var(--ink);font-family:var(--f-body);font-size:17px;line-height:1.62;
}
body::before{content:"";position:fixed;inset:0 0 auto;height:env(safe-area-inset-top,0px);z-index:10;background:var(--paper)}
a{color:var(--signal)}
:focus-visible{outline:2.5px solid var(--signal);outline-offset:2px;border-radius:4px}
.wrap{max-width:1180px;margin:0 auto;padding-left:max(16px,env(safe-area-inset-left,0px));padding-right:max(16px,env(safe-area-inset-right,0px))}

/* ---------- hero ---------- */
.hero{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.05fr);gap:40px;align-items:center;padding-block:56px 40px}
.kicker{font:600 .78rem/1.3 var(--f-mono);letter-spacing:.14em;text-transform:uppercase;color:var(--copper);margin:0 0 14px}
h1{font-family:var(--f-display);font-weight:700;font-size:clamp(2.5rem,6.2vw,4.4rem);line-height:1;letter-spacing:-.015em;margin:0 0 18px;text-wrap:balance}
h1 em{font-style:normal;color:var(--copper)}
.lead{font-size:1.15rem;max-width:34em;color:var(--ink);margin:0 0 24px}
.cta{display:flex;flex-wrap:wrap;gap:10px}
.hero .lab{margin:0}

/* ---------- shell ---------- */
.shell{display:grid;grid-template-columns:232px minmax(0,1fr);gap:48px;align-items:start}
.toc{position:sticky;top:calc(env(safe-area-inset-top,0px) + 84px);max-height:calc(100vh - 104px);overflow:auto;padding-block:8px 24px}
.toc-progress{font:600 .74rem var(--f-mono);letter-spacing:.06em;text-transform:uppercase;color:var(--muted);margin-bottom:18px}
.bar{height:6px;border-radius:3px;background:var(--line);margin-top:8px;overflow:hidden}
.bar i{display:block;height:100%;width:0;background:var(--ok);transition:width .4s}
.toc ol{list-style:none;margin:0;padding:0;display:flex;flex-direction:column;gap:2px}
.toc .grp{font:600 .7rem var(--f-mono);letter-spacing:.14em;text-transform:uppercase;color:var(--muted);margin:16px 0 4px}
.toc .grp:first-child{margin-top:0}
.toc a{display:flex;gap:10px;align-items:baseline;padding:6px 8px;border-radius:7px;color:var(--ink);text-decoration:none;font-size:.95rem;line-height:1.3}
.toc a:hover{background:var(--copper-soft)}
.toc a[aria-current="true"]{background:var(--ink);color:var(--panel)}
.toc a[aria-current="true"] .n{color:inherit}
.toc .n{font:600 .75rem var(--f-mono);color:var(--copper);min-width:1.6em}
.toc .chk{margin-left:auto;color:var(--ok);font-weight:700}
.toc a[aria-current="true"] .chk{color:inherit}
.toc a.done .chk::after{content:"✓"}

/* ---------- chapters ---------- */
main{min-width:0}
.ch{padding-block:56px;border-top:1px solid var(--line)}
.ch:first-child{border-top:0;padding-top:16px}
.ch-head{display:flex;gap:16px;align-items:flex-start;margin-bottom:18px}
.ch-num{font:600 .9rem var(--f-mono);color:var(--copper);border:1.5px solid var(--copper);border-radius:6px;padding:3px 8px;margin-top:8px;font-variant-numeric:tabular-nums}
.eyebrow{font:600 .74rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--muted);margin:0}
h2{font-family:var(--f-display);font-weight:700;font-size:clamp(1.75rem,3.4vw,2.45rem);line-height:1.12;margin:4px 0 0;text-wrap:balance}
h3{font-family:var(--f-display);font-weight:600;font-size:1.25rem;margin:28px 0 6px;text-wrap:balance}
.prose{max-width:66ch}
.prose p{margin:0 0 14px}
.prose ul{margin:0 0 14px;padding-left:1.2em}
.prose li{margin-bottom:6px}
.term-t{font-weight:700;color:var(--copper)}
.formula{font:600 1.25rem var(--f-mono);background:var(--panel);border:1px solid var(--line);border-radius:10px;padding:12px 16px;display:inline-block;margin:4px 0 16px;font-variant-numeric:tabular-nums}
.key{background:var(--copper-soft);border-radius:10px;padding:14px 18px;margin:24px 0 0;max-width:66ch}
.key b.tag{display:block;font:600 .72rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--copper);margin-bottom:4px}
.key p{margin:0}
.table-wrap{overflow-x:auto;margin:6px 0 16px;max-width:66ch}
table{border-collapse:collapse;width:100%;font-size:.95rem}
th,td{text-align:left;padding:8px 10px;border-bottom:1px solid var(--line);vertical-align:top}
th{font:600 .72rem var(--f-mono);letter-spacing:.1em;text-transform:uppercase;color:var(--muted)}
td.m{font-family:var(--f-mono);font-variant-numeric:tabular-nums;white-space:nowrap}
.done-btn{margin-top:28px}

/* ---------- bench / lab panel ---------- */
.lab{margin:28px 0 0;background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:20px;display:grid;grid-template-columns:minmax(0,1.35fr) minmax(0,1fr);gap:24px;box-shadow:0 1px 0 var(--line)}
.lab.stack{grid-template-columns:minmax(0,1fr)}
.lab-cap{grid-column:1/-1;display:flex;justify-content:space-between;gap:12px;flex-wrap:wrap;font:600 .72rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--muted);border-bottom:1px dashed var(--line);padding-bottom:10px}
.lab-cap span:last-child{color:var(--copper)}
.stage{min-width:0}
.stage svg{width:100%;height:auto;display:block;overflow:visible}
.controls{display:flex;flex-direction:column;gap:16px;min-width:0}
.ctl{display:flex;flex-direction:column;gap:4px}
.ctl label,.ctl .lbl-row{display:flex;justify-content:space-between;gap:8px;font-size:.9rem;font-weight:700}
.ctl output,.ctl .val{font:600 .9rem var(--f-mono);color:var(--copper);font-variant-numeric:tabular-nums}
input[type=range]{width:100%;accent-color:var(--copper);margin:4px 0}
input[type=number]{width:100%;font:600 1rem var(--f-mono);padding:7px 10px;border:1px solid var(--line);border-radius:8px;background:var(--paper);color:var(--ink)}
.meters{display:grid;grid-template-columns:repeat(auto-fit,minmax(112px,1fr));gap:8px}
.meter{background:var(--lcd-bg);color:var(--lcd-fg);border-radius:8px;padding:8px 10px;font-family:var(--f-mono);min-width:0}
.meter small{display:block;font-size:.66rem;letter-spacing:.09em;text-transform:uppercase;opacity:.78}
.meter b{display:block;font-size:1.12rem;font-weight:600;font-variant-numeric:tabular-nums;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.status{font-size:.95rem;margin:0;min-height:3.2em}
.warn{font-size:.88rem;color:var(--live);margin:0;font-weight:700}
.seg{display:flex;flex-wrap:wrap;gap:6px}
.seg button,.btn{font:700 .9rem var(--f-body);border:1.5px solid var(--ink);background:transparent;color:var(--ink);padding:7px 13px;border-radius:8px;cursor:pointer;transition:background .15s,color .15s}
.seg button:hover,.btn:hover{background:var(--copper-soft)}
.seg button[aria-pressed="true"]{background:var(--ink);color:var(--panel)}
.btn.primary{background:var(--copper);border-color:var(--copper);color:var(--on-copper)}
.btn.primary:hover{filter:brightness(1.08);background:var(--copper)}
.btn.done{border-color:var(--ok);color:var(--ok)}
.eq{font:600 .92rem var(--f-mono);color:var(--muted);margin:0;overflow-wrap:anywhere}
canvas{display:block;width:100%;border-radius:10px}

/* swatches for colour code */
.sw-row{display:flex;flex-wrap:wrap;gap:6px}
.sw{width:30px;height:30px;border-radius:50%;border:2px solid var(--line);cursor:pointer;padding:0}
.sw[aria-pressed="true"]{outline:3px solid var(--ink);outline-offset:2px}
.big-val{font:700 2rem var(--f-display);margin:0;line-height:1.1}

/* truth table */
.tt td,.tt th{text-align:center;font-family:var(--f-mono)}
.tt tr.cur td{background:var(--copper-soft);font-weight:700}

/* ---------- svg parts ---------- */
.wire{fill:none;stroke:var(--ink);stroke-width:2.5;stroke-linecap:round;stroke-linejoin:round;transition:opacity .3s}
.wire.off{opacity:.22}
.wire.flowpath{stroke:transparent}
.wire.hi{stroke:var(--signal);stroke-width:3.5}
.wire.lo{stroke:var(--lo)}
.cover{fill:var(--panel)}
.sym{fill:none;stroke:var(--ink);stroke-width:2.5;stroke-linecap:round;stroke-linejoin:round}
.sym.fill{fill:var(--panel)}
.plate{stroke:var(--ink);stroke-width:3;stroke-linecap:round}
.plate.thick{stroke-width:6}
.e{fill:var(--signal);transition:opacity .35s}
.e.idle{opacity:.28}
.lbl{fill:var(--muted);font:600 12px var(--f-mono)}
.lbl.ink{fill:var(--ink)}
.pol{fill:var(--live);font:700 13px var(--f-mono)}
.glow{fill:var(--glow);filter:blur(5px);transition:opacity .3s}
.heat{fill:var(--copper);filter:blur(4px);transition:opacity .3s}
.term{fill:var(--panel);stroke:var(--ink);stroke-width:2}
.lever{transition:transform .25s ease}
.switch{cursor:pointer}
.switch.open .lever{transform:rotate(-32deg)}
.removed{opacity:.3}
.removed .sym{stroke-dasharray:4 4}
.gate{fill:var(--panel);stroke:var(--ink);stroke-width:2.5;stroke-linejoin:round}
.tog{cursor:pointer}
.tog rect{fill:var(--line);stroke:var(--ink);stroke-width:2}
.tog circle{fill:var(--panel);stroke:var(--ink);stroke-width:2}
.tog.on rect{fill:var(--signal)}
.hint-click{cursor:pointer}
@media (prefers-reduced-motion: reduce){.lever,.e,.glow,.heat,.bar i{transition:none}}

.next{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:14px;margin-top:18px}
.next div{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:16px;min-width:0}
.next h4{font-family:var(--f-display);margin:0 0 6px;font-size:1.05rem}
.next p{margin:0;font-size:.95rem}
footer{border-top:1px solid var(--line);padding-block:28px 48px;color:var(--muted);font-size:.9rem}

/* ---------- responsive ---------- */
@media (max-width:920px){
  .hero{grid-template-columns:minmax(0,1fr);padding-block:32px 24px;gap:28px}
  .shell{grid-template-columns:minmax(0,1fr);gap:0}
  .toc{position:sticky;top:env(safe-area-inset-top,0px);z-index:5;background:var(--paper);max-height:none;overflow:visible;padding-block:10px;border-bottom:1px solid var(--line);margin-inline:calc(-1 * max(16px,env(safe-area-inset-left,0px)));padding-inline:max(16px,env(safe-area-inset-left,0px))}
  .toc-progress{margin-bottom:8px;display:flex;align-items:center;gap:10px}
  .toc-progress .bar{flex:1;margin-top:0}
  .toc ol{flex-direction:row;overflow-x:auto;gap:6px;padding-bottom:4px;scrollbar-width:thin}
  .toc .grp{display:none}
  .toc a{white-space:nowrap;border:1px solid var(--line);font-size:.85rem;padding:5px 9px}
  .toc .lbl-long{display:none}
}
@media (max-width:760px){
  body{font-size:16px}
  .lab{grid-template-columns:minmax(0,1fr);padding:14px;gap:18px}
  .ch{padding-block:40px}
}

/* =====================================================================
   Version 2 additions: site chrome, multi-page layouts, shared components
   ===================================================================== */

/* ---------- accessibility helpers ---------- */
.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}
.skip{position:absolute;left:-999px;top:8px;z-index:100;background:var(--ink);color:var(--panel);padding:8px 14px;border-radius:8px;font-weight:700}
.skip:focus{left:max(16px,env(safe-area-inset-left,0px))}

/* ---------- site header and footer: see "v4.0 navigation" below ---------- */

/* ---------- page heading ---------- */
.page-head{padding-block:40px 8px;max-width:760px}
.page-head h1{font-size:clamp(2.1rem,5vw,3.3rem);margin-bottom:12px}
.page-head .lead{margin-bottom:0}
.section{padding-block:40px;border-top:1px solid var(--line)}
.section:first-of-type{border-top:0}
.section > h2{margin-bottom:8px}
.section-intro{max-width:66ch;color:var(--muted);margin:0 0 20px}

/* ---------- entry points (home) ---------- */
.entry-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(min(100%,200px),1fr));gap:12px;margin-top:20px}
.entry{display:flex;flex-direction:column;gap:6px;padding:16px 18px;background:var(--panel);border:1px solid var(--line);border-radius:12px;color:var(--ink);text-decoration:none;min-width:0;transition:border-color .15s,transform .15s}
.entry:hover{border-color:var(--copper)}
.entry .k{font:600 .78rem var(--f-mono);color:var(--copper);letter-spacing:.1em;text-transform:uppercase}
.entry b{font:700 1.12rem/1.25 var(--f-display)}
.entry span:last-child{font-size:.93rem;color:var(--muted)}

/* ---------- resume + progress panel ---------- */
.resume{display:flex;flex-wrap:wrap;gap:12px 24px;align-items:center;justify-content:space-between;background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:16px 18px;margin-top:20px}
.resume p{margin:0}
.resume .meta{font:600 .78rem var(--f-mono);color:var(--muted);letter-spacing:.06em;text-transform:uppercase}

/* ---------- roadmap ---------- */
.road-stage{margin-top:28px}
.road-head{display:flex;gap:12px;align-items:baseline;flex-wrap:wrap;margin-bottom:10px}
.road-head h3{margin:0}
.road-head p{margin:0;color:var(--muted);font-size:.95rem}
.lessons{list-style:none;margin:0;padding:0;border:1px solid var(--line);border-radius:12px;background:var(--panel);overflow:hidden}
.lesson{display:grid;grid-template-columns:24px minmax(0,1fr) auto;gap:4px 14px;align-items:start;padding:14px 16px;border-top:1px solid var(--line)}
.lesson:first-child{border-top:0}
.lesson .dot{width:16px;height:16px;border-radius:50%;border:2px solid var(--line);margin-top:4px}
.lesson.done .dot{background:var(--ok);border-color:var(--ok)}
.lesson a.title{font-weight:700;color:var(--ink);text-decoration:none}
.lesson a.title:hover{text-decoration:underline;color:var(--copper)}
.lesson p{margin:2px 0 0;font-size:.93rem;color:var(--muted)}
.lesson .facts{display:flex;flex-wrap:wrap;gap:6px;justify-content:flex-end}
.lesson .pre{grid-column:2 / -1;font-size:.85rem;color:var(--muted)}
@media (max-width:640px){.lesson{grid-template-columns:24px minmax(0,1fr)}.lesson .facts{grid-column:2;justify-content:flex-start}}

/* ---------- pills, callouts ---------- */
.pill{display:inline-flex;align-items:center;gap:6px;font:600 .74rem var(--f-mono);letter-spacing:.04em;padding:3px 9px;border-radius:999px;border:1px solid var(--line);color:var(--muted);white-space:nowrap;background:var(--paper)}
.pill.ok{color:var(--ok);border-color:var(--ok);background:var(--ok-soft)}
.pill.caution{color:var(--caution);border-color:var(--caution);background:var(--caution-soft)}
.pill.danger{color:var(--live);border-color:var(--live);background:var(--danger-soft)}
.pill.big{font-size:.9rem;padding:6px 12px}
.callout{border-radius:10px;padding:12px 16px;margin:16px 0;max-width:66ch;background:var(--copper-soft)}
.callout b.tag{display:block;font:600 .72rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--copper);margin-bottom:4px}
.callout p{margin:0 0 6px}.callout p:last-child{margin:0}
.callout.safety{background:var(--danger-soft)}.callout.safety b.tag{color:var(--live)}
.callout.model{background:var(--paper);border:1px dashed var(--line)}.callout.model b.tag{color:var(--muted)}
.callout.ok{background:var(--ok-soft)}.callout.ok b.tag{color:var(--ok)}
.warn-list{list-style:none;padding:0;margin:0;display:flex;flex-direction:column;gap:8px}
.warn-list li{border-radius:8px;padding:8px 12px;font-size:.92rem}
.warn-list .danger{background:var(--danger-soft);color:var(--ink)}
.warn-list .danger b{color:var(--live)}
.warn-list .caution{background:var(--caution-soft)}
.warn-list .caution b{color:var(--caution)}

/* ---------- paired number + slider inputs ---------- */
.field{display:flex;flex-direction:column;gap:4px}
.field .row{display:grid;grid-template-columns:minmax(0,1fr) 112px;gap:10px;align-items:center}
.field label{font-size:.9rem;font-weight:700}
.field .num{display:flex;align-items:center;gap:6px}
.field .num input{width:100%;min-width:0;text-align:right;padding:6px 8px}
.field .num span{font:600 .85rem var(--f-mono);color:var(--muted);min-width:1.4em}
.field .help{font-size:.82rem;color:var(--muted);margin:0}
.field .err{font-size:.85rem;color:var(--live);margin:0;font-weight:700}
input[aria-invalid="true"]{border-color:var(--live);outline-color:var(--live)}
select{font:600 .95rem var(--f-body);padding:7px 10px;border:1px solid var(--line);border-radius:8px;background:var(--paper);color:var(--ink);max-width:100%}

/* ---------- calculation display ---------- */
.calc{font:500 .9rem/1.7 var(--f-mono);background:var(--paper);border:1px solid var(--line);border-radius:10px;padding:12px 14px;margin:0;overflow-x:auto;font-variant-numeric:tabular-nums}
.calc div{white-space:nowrap}
.calc .c{color:var(--muted)}

/* ---------- explainer layout ---------- */
.explain-2{display:grid;grid-template-columns:repeat(auto-fit,minmax(min(100%,280px),1fr));gap:14px;margin-top:20px}
.explain-2 > div{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:16px 18px;min-width:0}
.explain-2 h3{margin:0 0 6px;font-size:1.05rem}
.explain-2 p{margin:0 0 10px}.explain-2 p:last-child{margin:0}
.region-strip{display:flex;gap:6px;flex-wrap:wrap}
.led-lamp{width:46px;height:46px;border-radius:50%;border:2.5px solid var(--ink);background:var(--panel);position:relative;flex:none}
.led-lamp i{position:absolute;inset:-8px;border-radius:50%;background:var(--glow);filter:blur(8px);opacity:0}
.lamps{display:flex;gap:24px;align-items:center;flex-wrap:wrap}
.lamps figure{margin:0;display:flex;flex-direction:column;align-items:center;gap:6px;font-size:.82rem;color:var(--muted);text-align:center;max-width:150px}

/* ---------- components explorer ---------- */
.finder{display:flex;flex-wrap:wrap;gap:10px 16px;align-items:center;margin:20px 0 12px}
.finder input[type=search]{flex:1 1 260px;font:1rem var(--f-body);padding:10px 14px;border:1.5px solid var(--line);border-radius:10px;background:var(--panel);color:var(--ink)}
.finder input[type=search]:focus{border-color:var(--ink)}
.count{font:600 .8rem var(--f-mono);color:var(--muted)}
.comp-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(min(100%,210px),1fr));gap:10px;list-style:none;margin:0;padding:0}
.comp-card{display:flex;gap:12px;align-items:center;width:100%;text-align:left;padding:12px 14px;background:var(--panel);border:1px solid var(--line);border-radius:12px;color:var(--ink);cursor:pointer;font:inherit}
.comp-card:hover{border-color:var(--copper)}
.comp-card[aria-expanded="true"]{border-color:var(--ink);box-shadow:inset 0 0 0 1px var(--ink)}
.comp-card svg{width:56px;height:40px;flex:none}
.comp-card b{display:block;font-size:.98rem}
.comp-card small{display:block;color:var(--muted);font-size:.8rem}
.comp-detail{margin-top:20px;background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:20px;scroll-margin-top:16px}
.comp-detail header{display:flex;gap:18px;align-items:center;flex-wrap:wrap;border-bottom:1px dashed var(--line);padding-bottom:14px;margin-bottom:14px}
.comp-detail header svg{width:150px;height:96px;flex:none;background:var(--paper);border-radius:10px;border:1px solid var(--line)}
.comp-detail h2{margin:0}
.comp-detail .cat{font:600 .74rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--copper);margin:0}
.comp-cols{display:grid;grid-template-columns:repeat(auto-fit,minmax(min(100%,300px),1fr));gap:4px 28px}
.comp-cols h3{font-size:1.02rem;margin:14px 0 4px}
.comp-cols ul{margin:0;padding-left:1.15em}
.comp-cols li{margin-bottom:4px}
.comp-cols p{margin:0 0 8px}
.spec-note{font-size:.85rem;color:var(--muted)}
.empty{padding:24px;text-align:center;color:var(--muted);border:1px dashed var(--line);border-radius:12px}
.chips{display:flex;flex-wrap:wrap;gap:6px}
.chips button{font:600 .82rem var(--f-body);border:1.5px solid var(--line);background:var(--panel);color:var(--ink);padding:5px 11px;border-radius:999px;cursor:pointer}
.chips button[aria-pressed="true"]{background:var(--ink);border-color:var(--ink);color:var(--panel)}

/* ---------- quiz component ---------- */
.quiz-box{max-width:70ch;margin-top:20px}
.quiz-title{font:600 .74rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--copper);margin:0 0 10px}
.quiz-prev{font-size:.88rem;color:var(--muted);margin:-4px 0 10px}
.quiz-list{list-style:none;margin:0;padding:0;display:flex;flex-direction:column;gap:12px;counter-reset:q}
.quiz-list .q{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:14px 16px;counter-increment:q;scroll-margin-top:16px}
.quiz-list .q.is-right{border-color:var(--ok)}
.quiz-list .q.is-wrong{border-color:var(--live)}
.quiz-list fieldset{border:0;margin:0;padding:0;min-width:0}
.quiz-list legend{font-weight:700;padding:0;margin-bottom:8px}
.quiz-list legend::before{content:counter(q) ". ";color:var(--copper);font-family:var(--f-mono)}
.quiz-list .opts{display:flex;flex-direction:column;gap:4px}
.quiz-list .opts label{display:flex;gap:10px;align-items:flex-start;padding:6px 8px;border-radius:7px;cursor:pointer}
.quiz-list .opts input{margin-top:5px}
.quiz-list .opts label:hover{background:var(--copper-soft)}
.quiz-list .opts label.right{background:var(--ok-soft)}
.quiz-list .opts label.wrong{background:var(--danger-soft)}
.num-row{display:flex;gap:8px;align-items:center;flex-wrap:wrap}
.num-row input{width:9em;font:600 1rem var(--f-mono);padding:7px 10px;border:1px solid var(--line);border-radius:8px;background:var(--paper);color:var(--ink)}
.num-row .unit{font:600 .95rem var(--f-mono);color:var(--muted)}
.link-btn{background:none;border:0;padding:4px 0;margin-top:6px;color:var(--signal);font:700 .88rem var(--f-body);cursor:pointer;text-decoration:underline}
.hint{margin:4px 0 0;font-size:.92rem;background:var(--caution-soft);padding:8px 10px;border-radius:8px}
.fb{margin:8px 0 0;font-size:.94rem}
.is-right .fb b{color:var(--ok)}.is-wrong .fb b:first-child{color:var(--live)}
.quiz-summary{font:600 .95rem var(--f-mono);margin:14px 0 6px}
.quiz-review{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:14px 16px;margin:8px 0 12px}
.quiz-review ul{margin:0;padding-left:1.1em}
.quiz-review li{margin-bottom:8px;font-size:.94rem}
.check-block{margin-top:28px}
.check-block > summary{cursor:pointer;font:700 1rem var(--f-display);padding:10px 14px;border:1px solid var(--line);border-radius:10px;background:var(--panel);max-width:70ch}
.check-block[open] > summary{border-color:var(--ink)}

/* ---------- code ---------- */
pre.code{background:var(--code-bg);border:1px solid var(--line);border-radius:10px;padding:14px 16px;overflow-x:auto;font:500 .88rem/1.6 var(--f-mono);margin:8px 0 16px;max-width:76ch}
code{font-family:var(--f-mono);font-size:.92em}
p code,li code{background:var(--code-bg);padding:1px 5px;border-radius:4px}

/* ---------- misc ---------- */
.btn-row{display:flex;flex-wrap:wrap;gap:8px;align-items:center}
.confirm{display:flex;flex-wrap:wrap;gap:8px;align-items:center;font-size:.92rem}
.stat-row{display:flex;flex-wrap:wrap;gap:8px 18px;font:600 .82rem var(--f-mono);color:var(--muted)}
.prose-wide{max-width:72ch}
.chapters{min-width:0}

/* ---------- v2.1: lab switcher, signal pipeline, build steps ---------- */
.lab-switch{display:flex;flex-wrap:wrap;gap:6px;padding-top:20px}
.lab-switch a{font:600 .82rem var(--f-mono);padding:6px 12px;border:1.5px solid var(--line);border-radius:999px;color:var(--ink);text-decoration:none;background:var(--panel)}
.lab-switch a:hover{border-color:var(--copper)}
.lab-switch a[aria-current="page"]{background:var(--ink);border-color:var(--ink);color:var(--panel)}
.pipeline{list-style:none;margin:18px 0 0;padding:0;display:grid;grid-template-columns:repeat(auto-fit,minmax(min(100%,150px),1fr));gap:8px;counter-reset:st}
.pipeline li{background:var(--lcd-bg);color:var(--lcd-fg);border-radius:10px;padding:10px 12px;font-family:var(--f-mono);counter-increment:st;min-width:0}
.pipeline small{display:block;font-size:.66rem;letter-spacing:.09em;text-transform:uppercase;opacity:.8}
.pipeline small::before{content:counter(st) " · "}
.pipeline b{display:block;font-size:1.1rem;font-weight:600;font-variant-numeric:tabular-nums;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.pipeline span{display:block;font-size:.72rem;opacity:.8;margin-top:2px}
.steps{margin:0;padding-left:1.4em;max-width:70ch}
.steps li{margin-bottom:12px;padding-left:4px}
.steps li::marker{font:700 .95rem var(--f-mono);color:var(--copper)}
.two-inputs{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:10px}
.two-inputs select{width:100%}
.two-inputs input{width:100%;font:600 1rem var(--f-mono);padding:7px 10px;border:1px solid var(--line);border-radius:8px;background:var(--paper);color:var(--ink)}

/* ---------- v2.2: multimeter, fault cases, tasks ---------- */
.explain-2.three{grid-template-columns:repeat(auto-fit,minmax(min(100%,230px),1fr))}
.dmm{background:var(--ink);color:var(--panel);border-radius:16px;padding:14px;display:flex;flex-direction:column;gap:12px}
.dmm-screen{background:var(--lcd-bg);color:var(--lcd-fg);border-radius:8px;padding:10px 12px;font-family:var(--f-mono);min-height:72px;display:flex;flex-direction:column;justify-content:center}
.dmm-screen small{font-size:.68rem;letter-spacing:.1em;text-transform:uppercase;opacity:.8}
.dmm-screen b{font-size:1.9rem;font-weight:600;font-variant-numeric:tabular-nums;line-height:1.1;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.dial{display:grid;grid-template-columns:repeat(4,1fr);gap:6px}
.dial button{font:700 .9rem var(--f-mono);border:1.5px solid var(--panel);background:transparent;color:var(--panel);padding:8px 4px;border-radius:8px;cursor:pointer}
.dial button[aria-pressed="true"]{background:var(--glow);border-color:var(--glow);color:#1B1300}
.probe-row{display:grid;grid-template-columns:1fr 1fr;gap:10px}
.probe-row label{display:flex;flex-direction:column;gap:4px;font-size:.85rem;font-weight:700}
.probe-row select{width:100%}
.tp{cursor:pointer}
.tp circle.hit{fill:transparent}
.tp circle.dot{fill:var(--panel);stroke:var(--muted);stroke-width:2}
.tp:hover circle.dot,.tp:focus circle.dot{stroke:var(--ink);stroke-width:3}
.tp:focus{outline:none}
.tp:focus-visible circle.dot{stroke:var(--signal);stroke-width:3.5}
.tp.red circle.dot{fill:#D93025;stroke:#D93025}
.tp.black circle.dot{fill:var(--ink);stroke:var(--ink)}
.brk{cursor:pointer}
.brk rect{fill:var(--panel);stroke:var(--signal);stroke-width:1.5;stroke-dasharray:3 2}
.brk.on rect{fill:var(--glow);stroke:var(--ink);stroke-dasharray:none}
.clip-off{opacity:.35}
.tasks{list-style:none;margin:0;padding:0;display:flex;flex-direction:column;gap:6px;max-width:70ch}
.tasks li{display:flex;gap:10px;align-items:flex-start;padding:8px 12px;border:1px solid var(--line);border-radius:10px;background:var(--panel)}
.tasks li::before{content:"";flex:none;width:16px;height:16px;margin-top:3px;border-radius:50%;border:2px solid var(--line)}
.tasks li.done{border-color:var(--ok)}
.tasks li.done::before{background:var(--ok);border-color:var(--ok)}
.case{background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:18px;margin-top:14px}
.case > header{margin-bottom:12px}
.case h3{margin:2px 0 6px}
.case .cat{font:600 .74rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--copper);margin:0}
.case .lab{margin-top:8px;box-shadow:none}
.diag{border:1px solid var(--line);border-radius:12px;padding:12px 14px;margin:14px 0 10px;max-width:70ch}
.diag legend{font-weight:700;padding:0 4px}
.diag .opts{display:flex;flex-direction:column;gap:4px}
.diag label{display:flex;gap:10px;align-items:flex-start;padding:5px 6px;border-radius:7px;cursor:pointer}
.diag label:hover{background:var(--copper-soft)}
.chips button.solved{border-color:var(--ok)}
.chips button.solved::after{content:" ✓";color:var(--ok)}
.chips button[aria-pressed="true"].solved::after{color:inherit}
.log{margin:6px 0 0;padding-left:1.4em;font:500 .82rem var(--f-mono);max-height:180px;overflow:auto}
.review-card{display:flex;flex-wrap:wrap;gap:10px 20px;align-items:center;justify-content:space-between;background:var(--caution-soft);border-radius:12px;padding:14px 18px;margin-top:14px}
.review-card p{margin:0}
.code-box{display:flex;flex-direction:column;gap:8px;max-width:72ch;margin-top:12px}
.code-box textarea{width:100%;font:500 .85rem var(--f-mono);padding:8px 10px;border:1px solid var(--line);border-radius:8px;background:var(--paper);color:var(--ink);word-break:break-all}

/* ---------- v3.0: circuit sandbox ---------- */
.sb-toolbar{display:flex;flex-direction:column;gap:10px;margin-bottom:8px}
.sb-tools{display:flex;flex-wrap:wrap;gap:6px}
.sb-tools button{display:flex;align-items:center;gap:6px;font:700 .85rem var(--f-body);border:1.5px solid var(--line);background:var(--panel);color:var(--ink);padding:5px 10px 5px 6px;border-radius:9px;cursor:pointer}
.sb-tools button svg{width:34px;height:22px}
.sb-tools button:hover{border-color:var(--copper)}
.sb-tools button[aria-pressed="true"]{background:var(--ink);border-color:var(--ink);color:var(--panel)}
.sb-tools button[aria-pressed="true"] .sym{stroke:var(--panel)}
.sb-check{display:inline-flex;align-items:center;gap:6px;font-weight:700;font-size:.9rem}
.sb-main{display:grid;grid-template-columns:minmax(0,1fr) 280px;gap:16px;align-items:start}
@media (max-width:980px){.sb-main{grid-template-columns:minmax(0,1fr)}}
.sb-board{background:var(--panel);border:1px solid var(--line);border-radius:14px;overflow-x:auto}
.sb-board svg{display:block;width:100%;min-width:600px;height:auto;touch-action:manipulation}
.sb-side{display:flex;flex-direction:column;gap:10px;min-width:0}
.sb-props{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:12px 14px}
.sb-props h3{margin:0 0 6px;font-size:1.05rem}
.sb-props .field{margin-top:8px}
.sb-props .num input{text-align:left}
.sb-props p{margin:4px 0;font-size:.92rem}
.sb-read{font:600 .85rem/1.7 var(--f-mono);font-variant-numeric:tabular-nums}
.sb-files{margin-top:12px}
.sb-pt{fill:var(--line)}
.sb-hit{fill:transparent;cursor:crosshair}
.sb-pt.hot{fill:var(--copper)}
.sb-wire{stroke:var(--ink);stroke-width:3;stroke-linecap:round}
.sb-wire.hot{stroke:var(--live)}
.sb-whit{stroke:transparent;stroke-width:14;cursor:pointer}
.sb-part{cursor:pointer}
.sb-part .sb-phit{fill:transparent}
.sb-sel{fill:none;stroke:var(--signal);stroke-width:2;stroke-dasharray:5 4}
.sb-wire.sel{stroke:var(--signal)}
.sb-name{fill:var(--ink);font:700 12px var(--f-mono)}
.sb-val{fill:var(--muted);font:500 11px var(--f-mono)}
.sb-v,.sb-i{font:600 11px var(--f-mono);paint-order:stroke;stroke:var(--panel);stroke-width:3px;stroke-linejoin:round}
.sb-v{fill:var(--copper)}
.sb-i{fill:var(--signal)}
.sb-axis{fill:var(--muted);font:500 10px var(--f-mono);opacity:.7}
.sb-junction{fill:var(--ink)}
.sb-ghost{opacity:.45;pointer-events:none}
.sb-start{fill:var(--signal)}
.sb-e{fill:var(--signal)}
.sb-challenges li{flex-wrap:wrap}
.sb-challenges li > div{flex:1;min-width:0}
.sb-challenges b{display:block}
#sb-svg[data-tool="select"] .sb-hit,#sb-svg[data-tool="erase"] .sb-hit{pointer-events:none}
.sb-hit:hover{fill:var(--copper-soft)}
.sb-time{display:inline-flex;flex-wrap:wrap;gap:6px;align-items:center;padding:4px 8px;border:1.5px dashed var(--signal);border-radius:10px}
.sb-clock{font:600 .9rem var(--f-mono);font-variant-numeric:tabular-nums;min-width:7.5em}
#sb-chart{width:100%;display:block;border-radius:8px}
/* ---------- v3.2: grouped tools, oscilloscope, probes ---------- */
.sb-tools{gap:8px 14px}
.sb-group{display:flex;flex-wrap:wrap;gap:4px;align-items:center;padding:4px 6px;border:1px dashed var(--line);border-radius:10px}
.sb-glabel{font:600 .66rem var(--f-mono);letter-spacing:.1em;text-transform:uppercase;color:var(--muted);margin-right:2px}
.sb-scope #sb-scope{width:100%;display:block;border-radius:8px}
.sb-probe{fill:var(--scope-bg);font:700 11px var(--f-mono)}
.sb-spiked .sym{stroke:var(--live)}
@media (prefers-reduced-motion: no-preference){.sb-spiked{animation:sb-flash .5s ease-in-out 6 alternate}}
@keyframes sb-flash{from{opacity:1}to{opacity:.35}}
.sb-pin{fill:var(--muted);font:600 10px var(--f-mono)}
/* ---------- v3.3: breadboard trainer ---------- */
.bb-board{--bb-plastic:#F4F1EA;--bb-holec:#5E6660;--bb-strip:rgba(176,112,0,.16);--bb-case:rgba(0,0,0,.18)}
@media (prefers-color-scheme: dark){:root:not([data-theme="light"]) .bb-board{--bb-plastic:#1E2B25;--bb-holec:#0A100D;--bb-strip:rgba(242,181,74,.12);--bb-case:rgba(255,255,255,.45)}}
:root[data-theme="dark"] .bb-board{--bb-plastic:#1E2B25;--bb-holec:#0A100D;--bb-strip:rgba(242,181,74,.12);--bb-case:rgba(255,255,255,.45)}
.bb-board svg{min-width:640px}
.bb-bg{fill:var(--bb-plastic);stroke:var(--line);stroke-width:1.5}
.bb-gap{fill:var(--line);opacity:.8}
.bb-rail{stroke-width:2;opacity:.85}
.bb-rail.plus,.rail-plus{stroke:#D63A2F;fill:#D63A2F}
.bb-rail.minus,.rail-minus{stroke:#2F6FDB;fill:#2F6FDB}
.bb-lbl{fill:var(--muted);font:600 11px var(--f-mono)}
.bb-lbl.rail-plus,.bb-lbl.rail-minus{stroke:none;font-size:14px}
.bb-num{fill:var(--muted);font:500 9px var(--f-mono)}
.bb-strip{fill:var(--bb-strip)}
.bb-hole{fill:var(--bb-holec);transition:fill .1s}
.bb-hole.hot{fill:var(--copper)}
.bb-hit{fill:transparent;cursor:pointer}
.bb-hit:hover{fill:var(--copper-soft)}
#bb-svg.placing .bb-part{pointer-events:none}
#bb-svg.placing .bb-hit{cursor:crosshair}
.bb-part{cursor:pointer}
.bb-leg{stroke:#9AA3A0;stroke-width:2.2;stroke-linecap:round}
.bb-pinleg{fill:#B9C0BD}
.bb-lead{fill:none;stroke-width:3;stroke-linecap:round}
.bb-lead.red{stroke:#D63A2F}.bb-lead.black{stroke:#2A2A2A}
.bb-wire{fill:none;stroke-width:4;stroke-linecap:round}
.bb-wire-hit{fill:none;stroke:transparent;stroke-width:14}
.bb-end{fill:#B9C0BD}
.bb-body{stroke:rgba(0,0,0,.35);stroke-width:1}
.bb-part.sel .bb-body,.bb-part.sel .bb-wire{stroke:var(--signal);stroke-width:2.5;stroke-dasharray:4 2}
.bb-part.sel .bb-wire{stroke-dasharray:none;filter:drop-shadow(0 0 3px var(--signal))}
.bb-in{fill:#F4F4F4;font:700 9px var(--f-mono);pointer-events:none}
.bb-tiny{fill:var(--muted);font:700 9px var(--f-mono);pointer-events:none}
.bb-name{fill:var(--ink);font:700 10px var(--f-mono);paint-order:stroke;stroke:var(--bb-plastic);stroke-width:3px;pointer-events:none}
.bb-pick{fill:none;stroke:var(--signal);stroke-width:2.5}
.bb-preview{fill:none;stroke:var(--signal);stroke-width:2;stroke-dasharray:4 3}
#bb-ghost{pointer-events:none}
.bb-sw{display:inline-block;width:12px;height:12px;border-radius:3px;margin:0 2px 0 4px;border:1px solid rgba(0,0,0,.3)}
.bb-tools button{padding:6px 10px 6px 6px}
.bb-where{font:500 .82rem/1.6 var(--f-mono);color:var(--muted)}
.bb-legs{display:contents}
.warn-list .ok{background:var(--ok-soft)}
.bb-leg,.bb-end,.bb-pinleg,.bb-lead{pointer-events:none}
.bb-wire-case,.bb-lead.case{fill:none;stroke:var(--bb-case);stroke-width:6.5;stroke-linecap:round;pointer-events:none}
.bb-lead.case{stroke-width:5.5}
#fm-table td.m{white-space:normal}
/* ---------- v3.4: worksheets, certificate ---------- */
.ws-topics{border:1px solid var(--line);border-radius:12px;padding:10px 14px 12px;margin:0}
.ws-topics legend{font-weight:700;padding:0 6px}
.ws-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(210px,1fr));gap:6px 14px}
.ws-topic{display:flex;gap:6px;align-items:center}
.ws-sheet,.cert{background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:28px 32px;max-width:820px}
.ws-brand,.cert-brand{font:600 .74rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--muted);margin:0}
.ws-title{margin:4px 0 2px;font-size:1.5rem}
.ws-meta{margin:0;color:var(--muted);font-size:.9rem}
.ws-lines{display:flex;gap:24px;margin:18px 0 0}
.ws-lines span{flex:1;border-bottom:1.5px solid var(--ink);padding-bottom:2px;font-size:.85rem;color:var(--muted)}
.ws-lines span:last-child{flex:.5}
.ws-instr{margin:14px 0 6px;font-size:.92rem}
.ws-qs{padding-left:1.6em;margin:0;counter-reset:none}
.ws-q{margin:0 0 12px;padding-left:4px}
.ws-q p{margin:0 0 4px}
.ws-ans{color:var(--muted);font-size:.9rem}
.ws-blank{display:inline-block;min-width:9em;border-bottom:1.5px dotted var(--muted);margin:0 4px}
.ws-topic-h{list-style:none;margin:16px 0 6px -1.6em;font:700 .8rem var(--f-mono);letter-spacing:.08em;text-transform:uppercase;color:var(--copper)}
.ws-key{margin-top:28px;padding-top:18px;border-top:2px dashed var(--line)}
.ws-key .ws-qs{margin-top:10px}
.ws-work{font-size:.88rem;color:var(--muted)}
.cert{text-align:center;border:3px double var(--copper)}
.cert-title{font-size:2rem;margin:6px 0 14px}
.cert-line{margin:6px auto;max-width:56ch}
.cert-name{font:600 1.7rem var(--f-display);margin:8px auto;min-width:60%;display:inline-block;border-bottom:1.5px solid var(--ink);padding:0 12px 2px}
.cert-stats{display:flex;flex-wrap:wrap;justify-content:center;gap:6px 18px;margin:16px 0;font-size:.92rem}
.cert-stages{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:4px 20px;text-align:left;margin-top:12px}
.cert-stages h3{font-size:.9rem;margin:10px 0 4px}
.cert-stages ul{list-style:none;padding:0;margin:0;font-size:.85rem}
.cert-stages li{color:var(--muted)}
.cert-stages li.done{color:var(--ink)}
.cert-date{margin:18px 0 4px;font-weight:700}
.cert-note{font-size:.78rem;color:var(--muted);margin:0}
@media (max-width:600px){.ws-sheet,.cert{padding:18px 16px}}

/* ---------- print (every page) ---------- */
@media print{
  :root,:root[data-theme="dark"],:root:not([data-theme="light"]){
    --paper:#fff;--panel:#fff;--ink:#000;--muted:#444;--line:#bbb;--grid:transparent;--copper:#7a3a10;--signal:#1C5BC9;--live:#C42F2A;--ok:#1B7A49;
    color-scheme:light;
  }
  @page{margin:16mm 14mm}
  body{background:#fff!important;color:#000;font-size:11pt}
  .site-head .site-nav,.menu-btn,.theme-btn,.skip,.site-foot,.no-print,.lab-switch,.btn,.done-btn,.sb-toolbar,.chips,.confirm{display:none!important}
  .site-head{position:static;border:0;padding:0}
  main{padding:0!important}
  a{color:inherit;text-decoration:none}
  .section{padding:0;margin:0 0 12pt;border:0}
  .card,.ws-q,.cert-stages > div,tr,li,figure,.meter{break-inside:avoid}
  h1,h2,h3{break-after:avoid}
  .ws-sheet,.cert{border:0;padding:0;max-width:none;border-radius:0}
  .cert{border:3px double #7a3a10;padding:18mm 14mm;min-height:240mm}
  .ws-key{break-before:page;border:0;margin:0;padding:0}
  .ws-preview > h2{display:none}
  .ws-blank{min-width:12em}
  .ws-q{margin-bottom:16pt}
}
/* ---------- v3.4: speed drills ---------- */
.dr-bar{display:flex;flex-wrap:wrap;gap:8px;align-items:center;margin-bottom:10px}
.dr-bar .pill.caution{background:var(--caution-soft);color:var(--caution)}
.dr-card{background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:18px 20px;max-width:720px}
.dr-res{width:min(100%,320px);height:auto;display:block;margin:0 0 6px}
.dr-q{font-size:1.15rem;font-weight:700;margin:0 0 12px}
.dr-form{display:flex;flex-wrap:wrap;gap:8px;align-items:center}
.dr-form input{font:600 1.15rem var(--f-mono);width:10em;max-width:100%;padding:8px 10px;border:1.5px solid var(--line);border-radius:9px;background:var(--paper);color:var(--ink)}
.dr-form input:focus{outline:3px solid var(--signal);outline-offset:1px}
.dr-unit{font:600 1rem var(--f-mono);color:var(--muted);min-width:2.5em}
.dr-fb{min-height:1.5em;margin:12px 0 0;font-size:.95rem}
.dr-fb.ok{color:var(--ok)}
.dr-fb.bad{color:var(--live)}
.dr-result{font-size:1.15rem;font-weight:700}
.dr-missed{padding-left:1.4em}
.dr-missed li{margin-bottom:8px}
.dr-missed p{margin:0}
/* ---------- v3.5: hardware lab, serial monitor, what's new ---------- */
.hw-safety li{margin-bottom:4px}
.hw-code summary{cursor:pointer;font-weight:700}
.hw-code pre{max-height:420px;overflow:auto;max-width:none}
.hw-simbox{border:1.5px dashed var(--signal);border-radius:12px;padding:10px 14px;margin-top:8px;background:var(--panel)}
.hw-simbox p{margin:0 0 6px}
.hw-meters{grid-template-columns:repeat(auto-fill,minmax(120px,1fr))}
.hw-meters small{display:flex;align-items:center;gap:4px}
.hw-raw{display:block;font:500 .72rem var(--f-mono);color:var(--muted)}
.hw-chart-wrap{margin:12px 0}
.hw-chart{display:block;width:100%;height:260px;border-radius:10px}
.hw-controls{display:grid;grid-template-columns:repeat(auto-fit,minmax(200px,1fr));gap:10px 18px;align-items:end;max-width:820px}
.hw-exp{border:1px solid var(--line);border-radius:14px;padding:14px 18px;margin:0 0 14px;background:var(--panel);max-width:880px}
.hw-exp h3{margin:0 0 6px}
.hw-exp p{margin:6px 0}
.hw-out{font-size:.95rem;border-left:3px solid var(--copper);padding-left:10px}
.hw-key{display:inline-flex;align-items:center;gap:6px;font-size:.88rem;margin-right:10px}
.hw-key i{display:inline-block;width:18px;height:4px;border-radius:2px}
.hw-log{max-height:260px;overflow:auto;max-width:none}
.hw-legend{min-height:1.4em}
.sm-out{height:340px;overflow:auto;max-width:none;white-space:pre-wrap;word-break:break-word}
.sm-form{display:flex;gap:8px;flex-wrap:wrap}
.sm-form input{flex:1;min-width:0;font:500 .95rem var(--f-mono);padding:8px 10px;border:1.5px solid var(--line);border-radius:9px;background:var(--paper);color:var(--ink)}
.wn-list{list-style:none;padding:0;margin:0;max-width:820px;border-left:2px solid var(--line)}
.wn-item{position:relative;padding:0 0 22px 22px}
.wn-item::before{content:"";position:absolute;left:-7px;top:8px;width:12px;height:12px;border-radius:50%;background:var(--panel);border:2px solid var(--copper)}
.wn-item:first-child::before{background:var(--copper)}
.wn-head{display:flex;flex-wrap:wrap;align-items:baseline;gap:6px 12px}
.wn-head h2{margin:0;font-size:1.3rem}
.wn-head time{color:var(--muted);font:500 .85rem var(--f-mono)}
.wn-item ul{margin:8px 0 0;padding-left:1.2em}
.wn-item li{margin-bottom:4px}
.hw-sw{display:inline-block;width:14px;height:4px;border-radius:2px;margin-left:4px}
/* ---------- v3.6: real-build check ---------- */
.rc-table input{width:7em}
.rc-table td{vertical-align:middle}
.rc-exp{font:500 .8rem var(--f-mono);color:var(--muted);white-space:nowrap}
.rc-result{margin-top:12px;max-width:80ch}
.rc-causes{padding-left:1.4em}
.rc-causes li{margin-bottom:4px}
.rc-good{background:var(--ok-soft);border-radius:8px;padding:8px 12px}
/* ---------- v3.7: op-amps ---------- */
.oa-w{fill:none;stroke:var(--ink);stroke-width:2;stroke-linejoin:round;stroke-linecap:round}
.oa-tri{fill:var(--panel);stroke-width:2.5}
.oa-src{fill:var(--panel)}
.oa-dot{fill:var(--ink)}
.oa-t{fill:var(--ink);font:700 11px var(--f-mono)}
.oa-pin{fill:var(--ink);font:700 16px var(--f-mono)}
.oa-l{fill:var(--muted);font:600 11px var(--f-mono)}
.oa-v{fill:var(--copper);font:700 12px var(--f-mono);paint-order:stroke;stroke:var(--panel);stroke-width:3px}
.oa-explain{font-size:.95rem}
/* ---------- v3.8: digital logic lab ---------- */
.lg-sym{fill:var(--panel);stroke:var(--ink);stroke-width:2.5;stroke-linejoin:round}
.lg-wire{fill:none;stroke-width:4;stroke-linecap:round}
.lg-led{stroke:var(--ink);stroke-width:2}
.lg-lbl{fill:var(--ink);font:700 13px var(--f-mono)}
.lg-val{fill:var(--copper);font:700 13px var(--f-mono)}
.lg-name{fill:var(--muted);font:700 13px var(--f-mono);letter-spacing:.1em}
.lg-bit[aria-pressed="true"]{background:var(--ok-soft);border-color:var(--ok)}
.lg-rule{font-size:.98rem}
.lg-table{max-width:320px}
.lg-table td,.lg-table th{text-align:center}
.lg-table tr.cur td{background:var(--copper-soft)}
.lg-table.small{font-size:.85rem;margin-top:8px}
.lg-nand{display:grid;grid-template-columns:repeat(auto-fit,minmax(240px,1fr));gap:14px}
.lg-card{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:12px 14px}
.lg-card h3{margin:0 0 4px;font-size:1.05rem}
.lg-card p{margin:0 0 8px;font-size:.9rem}
.lg-chipout{font:700 .85rem var(--f-mono);padding:4px 10px;border:1.5px solid var(--ink);border-radius:8px}
.lg-addlabel{margin:10px 0 4px;font:600 .72rem var(--f-mono);letter-spacing:.1em;text-transform:uppercase;color:var(--muted)}
.lg-bits{display:flex;gap:6px}
.lg-bitbtn,.lg-o{width:52px;min-height:44px;display:inline-flex;flex-direction:column;align-items:center;justify-content:center;font:700 1.2rem var(--f-mono);border-radius:8px}
.lg-bitbtn{border:1.5px solid var(--ink);background:var(--panel);color:var(--ink);cursor:pointer}
.lg-bitbtn[aria-pressed="true"]{background:var(--ok-soft);border-color:var(--ok)}
.lg-bitbtn small{font:500 .62rem var(--f-mono);color:var(--muted)}
.lg-out .lg-o{border:1px dashed var(--line)}
.lg-carry{color:var(--copper);font-size:.95rem;min-height:26px}
#lg-c .lg-o{min-height:26px;border:0}
.lg-co{color:var(--copper)}
.lg-sum{font:700 1.1rem var(--f-mono);margin:10px 0}
.lg-state{min-height:2.6em}
.lg-chart{display:block;width:100%;border-radius:10px}
.lc-leds{display:flex;gap:14px;margin:6px 0}
.lc-led{display:flex;flex-direction:column;align-items:center;gap:4px;font:600 .75rem var(--f-mono);color:var(--muted)}
.lc-led i{width:34px;height:34px;border-radius:50%;border:2px solid var(--ink);background:var(--panel)}
.lc-led.on i{background:#FF3B30;box-shadow:0 0 14px #FF3B30}
@media (max-width:600px){.lg-bitbtn,.lg-o{width:44px}}
/* ---------- v3.9: teacher pack ---------- */
.tp-plan td{vertical-align:top}
.tp-sheet{margin-bottom:24px}
.tp-sheet h3{font-size:1rem;margin:14px 0 4px}
.tp-sheet ul,.tp-sheet ol{margin:0;padding-left:1.3em}
.tp-two{display:grid;grid-template-columns:repeat(auto-fit,minmax(240px,1fr));gap:4px 24px}
.tp-safety{border-left:3px solid var(--live);padding-left:10px}
.tp-results{width:100%;border-collapse:collapse;margin-top:4px}
.tp-results th,.tp-results td{border:1px solid var(--line);padding:8px;text-align:left;height:2.2em}
.tp-line{display:block;border-bottom:1px dotted var(--muted);height:1.6em}
.tp-notes{margin-top:14px;padding:8px 12px;border:1.5px dashed var(--copper);border-radius:8px}
.tp-bad{color:var(--live)}
#tp-codes{width:100%;font:500 .85rem var(--f-mono)}
@media print{.tp-sheet{break-after:page;border:0;padding:0}.tp-sheet:last-child{break-after:auto}.tp-results th,.tp-results td{border-color:#888}}

/* =====================================================================
   v4.0 navigation, footer and home page
   ===================================================================== */
.g-learn{--g:var(--copper)} .g-build{--g:var(--signal)} .g-projects{--g:var(--caution)} .g-practise{--g:var(--ok)} .g-teach{--g:var(--violet)}
.i{width:20px;height:20px;flex:none;fill:none;stroke:currentColor;stroke-width:1.8;stroke-linecap:round;stroke-linejoin:round}

/* ---------- header ---------- */
.site-head{position:sticky;top:0;z-index:50;background:color-mix(in srgb,var(--paper) 88%,transparent);backdrop-filter:saturate(1.4) blur(10px);-webkit-backdrop-filter:saturate(1.4) blur(10px);border-bottom:1px solid var(--line)}
@supports not (background:color-mix(in srgb,red 50%,blue)){.site-head{background:var(--paper)}}
.head-in{display:flex;align-items:center;gap:8px 14px;min-height:64px}
.site-head .wrap{max-width:1320px}
.brand{display:inline-flex;align-items:center;gap:10px;font:700 1.05rem var(--f-display);color:var(--ink);text-decoration:none;letter-spacing:.01em;white-space:nowrap;margin-right:6px}
.brand svg{width:30px;height:30px;flex:none}
.site-nav{flex:1;min-width:0;display:flex;align-items:center;gap:8px}
.nav-groups{display:flex;gap:2px;list-style:none;margin:0;padding:0}
.nav-group{position:relative}
.nav-top{display:flex;align-items:center;gap:6px;font:700 .95rem var(--f-body);color:var(--ink);background:none;border:0;border-radius:9px;padding:9px 9px;cursor:pointer}
.nav-top .i{width:18px;height:18px;color:var(--g)}
.nav-top .chev{width:14px;height:14px;color:var(--muted);transition:transform .15s}
.nav-top:hover,.nav-top[aria-expanded="true"]{background:var(--copper-soft)}
.nav-top[aria-expanded="true"] .chev{transform:rotate(180deg)}
.nav-group.is-current>.nav-top{box-shadow:inset 0 -3px 0 var(--g)}
.nav-panel{position:absolute;left:0;top:calc(100% + 8px);width:min(400px,90vw);background:var(--panel);border:1px solid var(--line);border-top:3px solid var(--g);border-radius:12px;box-shadow:0 16px 40px rgba(0,0,0,.14);padding:14px;z-index:60;display:none}
.nav-group:last-child .nav-panel{left:auto;right:0}
.nav-group:hover>.nav-panel,.nav-group:focus-within>.nav-panel{display:block}
html.js .nav-group:hover>.nav-panel,html.js .nav-group:focus-within>.nav-panel{display:none}
html.js .nav-top[aria-expanded="true"]+.nav-panel{display:block}
.nav-blurb{margin:0 6px 8px;font-size:.85rem;color:var(--muted)}
.nav-panel ul{list-style:none;margin:0;padding:0;display:grid;gap:2px}
.nav-panel a{display:block;padding:8px 10px;border-radius:8px;color:var(--ink);text-decoration:none}
.nav-panel a b{display:block;font-size:.95rem}
.nav-panel a span{display:block;font-size:.84rem;color:var(--muted);line-height:1.35}
.nav-panel a:hover{background:var(--copper-soft)}
.nav-panel a[aria-current="page"]{background:color-mix(in srgb,var(--g) 14%,transparent);box-shadow:inset 3px 0 0 var(--g)}
.nav-utils{display:flex;gap:2px;margin-left:auto}
.nav-util{position:relative;display:flex;align-items:center;gap:7px;padding:9px 10px;border-radius:9px;color:var(--ink);text-decoration:none;font-weight:700;font-size:.9rem;white-space:nowrap}
.nav-util .i{width:18px;height:18px;color:var(--muted)}
.nav-util:hover{background:var(--copper-soft)}
.nav-util.is-current{box-shadow:inset 0 -3px 0 var(--ink)}
.nav-badge{min-width:20px;height:20px;padding:0 6px;border-radius:999px;background:var(--copper);color:var(--on-copper);font:700 .72rem/20px var(--f-mono);text-align:center}
.nav-dot{width:8px;height:8px;border-radius:50%;background:var(--live);display:inline-block;align-self:flex-start;margin-top:2px}
.nav-dot[hidden],.nav-badge[hidden]{display:none}
.menu-btn{display:none;align-items:center;gap:6px;margin-left:auto;font:700 .9rem var(--f-body);color:var(--ink);background:var(--panel);border:1.5px solid var(--line);border-radius:10px;padding:7px 12px;cursor:pointer}
.theme-btn{display:inline-grid;place-items:center;width:38px;height:38px;flex:none;border:1.5px solid var(--line);background:var(--panel);color:var(--ink);border-radius:50%;padding:0;cursor:pointer;font:600 .7rem var(--f-mono)}
.theme-btn .i{width:18px;height:18px}
.theme-btn:hover,.menu-btn:hover{border-color:var(--ink)}
/* utilities show icons only on mid-size screens */
@media (max-width:1365px) and (min-width:1024px){.nav-util span:not(.nav-badge):not(.nav-dot):not(.sr-only){position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0,0,0,0)}.nav-top{padding:9px 8px}}
@media (max-width:1023px){
  html.js .menu-btn{display:inline-flex}
  html.js .site-nav{display:none}
  .head-in{flex-wrap:wrap}
  .site-nav{flex-basis:100%;flex-direction:column;align-items:stretch;padding-bottom:12px}
  html.js .site-head.nav-open .site-nav{display:flex;max-height:calc(100vh - 70px);overflow:auto}
  .nav-groups{flex-direction:column;gap:14px}
  .nav-top{pointer-events:none;padding:4px 2px;font-size:.78rem;letter-spacing:.12em;text-transform:uppercase;color:var(--muted)}
  .nav-top .chev{display:none}
  .nav-group.is-current>.nav-top{box-shadow:none;color:var(--g)}
  .nav-panel,html.js .nav-panel{display:block!important;position:static;width:auto;box-shadow:none;border:0;border-left:3px solid var(--g);border-radius:0;padding:0 0 0 8px}
  .nav-blurb,.nav-panel a span{display:none}
  .nav-panel ul{grid-template-columns:repeat(auto-fill,minmax(200px,1fr))}
  .nav-panel a{padding:9px 10px}
  .nav-utils{margin:6px 0 0;border-top:1px solid var(--line);padding-top:10px;flex-wrap:wrap}
  .menu-btn{order:1}
  .theme-btn{order:2}
  .site-nav{order:3}
  .nav-utils{order:-1;margin:0 0 4px;border-top:0;padding-top:0;border-bottom:1px solid var(--line);padding-bottom:10px}
  .brand span{font-size:.98rem}
}
html.menu-lock{overflow:hidden}
@media (max-width:1023px){.site-head{position:relative}html{scroll-padding-top:calc(env(safe-area-inset-top,0px) + 16px)}}

/* ---------- footer ---------- */
.site-foot{border-top:1px solid var(--line);margin-top:72px;padding-block:44px 56px;color:var(--muted);font-size:.9rem;background:var(--panel)}
.foot-grid{display:grid;grid-template-columns:1.4fr repeat(5,1fr);gap:28px 24px}
.foot-about p{margin:12px 0;max-width:34ch}
.foot-col h2{display:flex;align-items:center;gap:8px;font:700 .78rem var(--f-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--ink);margin:6px 0 10px}
.foot-col h2 .i{width:16px;height:16px;color:var(--g)}
.site-foot ul{list-style:none;margin:0;padding:0;display:grid;gap:6px}
.site-foot a{color:var(--ink);text-decoration:none}
.site-foot a:hover{color:var(--copper);text-decoration:underline}
.foot-links{margin-top:8px!important}
.foot-ver{font:600 .7rem var(--f-mono);color:var(--muted);border:1px solid var(--line);border-radius:999px;padding:1px 7px;margin-left:4px}
.foot-notes{border-top:1px solid var(--line);margin-top:32px;padding-top:18px}
.foot-notes p{margin:0 0 6px;max-width:90ch}
@media (max-width:1023px){.foot-grid{grid-template-columns:repeat(auto-fill,minmax(160px,1fr))}.foot-about{grid-column:1/-1}}

/* ---------- home ---------- */
.home-hero{border-bottom:1px solid var(--line);background:linear-gradient(180deg,transparent,color-mix(in srgb,var(--panel) 70%,transparent))}
.hero-grid{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.02fr);gap:48px;align-items:center;padding-block:64px 56px}
.hero-copy .lead{font-size:1.2rem}
.btn.big{padding:11px 20px;font-size:1rem}
.hero-lab{margin:0}
.trust{display:flex;flex-wrap:wrap;gap:8px 18px;list-style:none;margin:22px 0 0;padding:0;font:600 .8rem var(--f-mono);color:var(--muted)}
.trust li::before{content:"✓";color:var(--ok);margin-right:6px}
.home-sec{padding-top:56px}
.sec-head{display:flex;flex-wrap:wrap;align-items:baseline;justify-content:space-between;gap:6px 20px;margin-bottom:20px}
.sec-head h2{margin:0}
.sec-head p{margin:0;color:var(--muted);flex-basis:100%}
.more{font-weight:700;text-decoration:none}
.more::after{content:" →"}
.continue{display:flex;gap:22px;align-items:center;margin-top:36px;padding:20px 24px;background:var(--panel);border:1px solid var(--line);border-left:4px solid var(--ok);border-radius:14px}
.continue h2{margin:0 0 4px;font-size:1.4rem}
.continue p{margin:0 0 12px}
.cont-ring{width:92px;flex:none}
.ring{display:block;width:100%;height:auto}
.ring-bg{fill:none;stroke:var(--line);stroke-width:8}
.ring-fg{fill:none;stroke:var(--ok);stroke-width:8;stroke-linecap:round;transform:rotate(-90deg);transform-origin:40px 40px;transition:stroke-dasharray .6s}
.ring-big{fill:var(--ink);font:700 15px var(--f-mono)}
.ring-small{fill:var(--muted);font:600 9px var(--f-mono)}
.paths{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:14px}
.path,.area,.tool,.news-card{background:var(--panel);border:1px solid var(--line);border-radius:14px;color:var(--ink);text-decoration:none;transition:border-color .15s,transform .15s,box-shadow .15s}
.path{display:flex;flex-direction:column;gap:6px;padding:18px}
.path-k{font:600 .74rem var(--f-mono);letter-spacing:.1em;text-transform:uppercase;color:var(--copper)}
.path b{font:700 1.15rem/1.25 var(--f-display)}
.path span:last-child{color:var(--muted);font-size:.93rem}
a.path:hover,a.tool:hover,a.news-card:hover{border-color:var(--copper);transform:translateY(-2px);box-shadow:0 8px 24px rgba(0,0,0,.07)}
.area-grid{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:14px}
.area{padding:18px;border-top:4px solid var(--g)}
.area-ico{width:40px;height:40px;border-radius:10px;display:grid;place-items:center;background:color-mix(in srgb,var(--g) 14%,transparent);color:var(--g);margin-bottom:10px}
.area-ico .i{width:22px;height:22px}
.area h3{margin:0 0 4px;font-size:1.2rem}
.area p{margin:0 0 10px;color:var(--muted);font-size:.9rem}
.area ul{list-style:none;margin:0;padding:0;display:grid;gap:4px}
.area a{color:var(--ink);font-weight:700;font-size:.92rem;text-decoration:none}
.area a::before{content:"›";color:var(--g);margin-right:6px}
.area a:hover{color:var(--g);text-decoration:underline}
.news-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px}
.news-card{display:flex;flex-direction:column;gap:8px;padding:16px 18px}
.news-meta{display:flex;align-items:center;gap:10px;font:600 .78rem var(--f-mono);color:var(--muted)}
.news-card b{font:700 1.1rem/1.3 var(--f-display)}
.news-tag{font-size:.85rem;color:var(--muted);margin-top:auto}
.tools{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px}
.tool{display:flex;flex-direction:column;gap:6px;padding:0 0 18px;overflow:hidden}
.tool b{font:700 1.15rem var(--f-display);padding:0 18px}
.tool>span{color:var(--muted);font-size:.93rem;padding:0 18px}
.tool-art{display:block;width:100%;height:auto;background:color-mix(in srgb,var(--g) 7%,var(--paper));border-bottom:1px solid var(--line);margin-bottom:8px}
.ta-grid path{stroke:var(--line);stroke-width:1}
.ta-w{fill:none;stroke:var(--ink);stroke-width:2.5;stroke-linejoin:round}
.ta-led{fill:#FF3B30;stroke:var(--ink);stroke-width:2}
.ta-e{fill:var(--signal)}
.ta-board{fill:var(--panel);stroke:var(--line);stroke-width:1.5}
.ta-holes circle{fill:var(--muted);opacity:.5}
.ta-rail-p{stroke:#D63A2F;stroke-width:2}.ta-rail-n{stroke:#2F6FDB;stroke-width:2}
.ta-wire{fill:none;stroke:#1F9D55;stroke-width:3.5;stroke-linecap:round}
.ta-res{fill:#D9B98A;stroke:rgba(0,0,0,.3)}
.ta-ledc{fill:#FF3B30;stroke:rgba(0,0,0,.3)}
.ta-pcb{fill:#11766E;opacity:.9}.ta-usb{fill:#9AA3A0}.ta-chip{fill:#1C1C1C}
.ta-pins path{stroke:#E5E5E5;stroke-width:3;stroke-dasharray:3 4}
.ta-plot{fill:none;stroke:var(--caution);stroke-width:3;stroke-linecap:round}
.ta-axis{fill:none;stroke:var(--muted);stroke-width:1.5}
.stages{list-style:none;margin:0;padding:0;display:grid;gap:10px}
.stage a{display:grid;grid-template-columns:44px minmax(0,1fr) auto;gap:6px 16px;align-items:center;padding:14px 18px;background:var(--panel);border:1px solid var(--line);border-radius:12px;color:var(--ink);text-decoration:none}
.stage a:hover{border-color:var(--copper)}
.stage-n{width:36px;height:36px;border-radius:50%;display:grid;place-items:center;background:var(--ink);color:var(--panel);font:700 1rem var(--f-mono)}
.stage-body b{display:block;font-size:1.05rem}
.stage-body>span:not(.stage-bar){display:block;color:var(--muted);font-size:.9rem}
.stage-bar{display:block;height:6px;border-radius:3px;background:var(--line);margin-top:8px;overflow:hidden}
.stage-bar i{display:block;height:100%;background:var(--ok)}
.stage-meta{font:600 .8rem var(--f-mono);color:var(--muted);text-align:right;white-space:nowrap}
.principles{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:24px;border-top:1px solid var(--line);margin-top:56px}
.principles h3{margin:0 0 6px;font-size:1.05rem}
.principles p{margin:0;color:var(--muted);font-size:.93rem}
@media (max-width:1100px){.area-grid{grid-template-columns:repeat(3,minmax(0,1fr))}.paths{grid-template-columns:repeat(2,minmax(0,1fr))}}
@media (max-width:860px){.hero-grid{grid-template-columns:minmax(0,1fr);gap:28px;padding-block:36px 32px}.news-grid,.tools{grid-template-columns:minmax(0,1fr)}.area-grid{grid-template-columns:repeat(2,minmax(0,1fr))}.principles{grid-template-columns:minmax(0,1fr)}}
@media (max-width:560px){.paths,.area-grid{grid-template-columns:minmax(0,1fr)}.continue{flex-direction:column;align-items:flex-start}.stage a{grid-template-columns:36px minmax(0,1fr)}.stage-meta{grid-column:2;text-align:left}.home-sec{padding-top:40px}}

/* ---------- roadmap and progress pages ---------- */
.road-tools{display:flex;flex-wrap:wrap;gap:12px 24px;align-items:center;margin-top:8px}
.road-jump{display:flex;flex-wrap:wrap;gap:6px;margin:16px 0 0}
.road-jump a{font:600 .82rem var(--f-mono);padding:6px 12px;border:1.5px solid var(--line);border-radius:999px;color:var(--ink);text-decoration:none;background:var(--panel)}
.road-jump a:hover{border-color:var(--copper)}
.road-stage{scroll-margin-top:84px}
.prog-top{display:flex;gap:28px;align-items:center;flex-wrap:wrap}
.prog-ring{width:132px;flex:none}
.prog-top>div:last-child{flex:1;min-width:min(100%,260px)}
.prog-meters{max-width:720px}
.wn-headline{margin:6px 0 0;font-weight:700}
@media (prefers-reduced-motion:reduce){a.path:hover,a.tool:hover,a.news-card:hover{transform:none}.ring-fg{transition:none}}
@media print{.site-head{position:static;backdrop-filter:none}.home-hero{background:none}}
@media (max-width:440px){.brand{gap:8px}.brand svg{width:28px;height:28px}.menu-btn{padding:8px 9px}.menu-btn span{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0,0,0,0)}.head-in{gap:8px 10px}}

/* =====================================================================
   v4.1 search and glossary
   ===================================================================== */
.search-btn{display:inline-flex;align-items:center;gap:8px;height:38px;padding:0 8px 0 10px;border:1.5px solid var(--line);border-radius:10px;background:var(--panel);color:var(--muted);text-decoration:none;font:600 .88rem var(--f-body);white-space:nowrap;flex:none}
.search-btn:hover{border-color:var(--ink);color:var(--ink)}
.search-btn .i{width:18px;height:18px}
.search-btn kbd,.sx kbd{font:600 .72rem var(--f-mono);border:1px solid var(--line);border-bottom-width:2px;border-radius:5px;padding:1px 6px;color:var(--muted);background:var(--paper)}
.search-label{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0,0,0,0)}.search-btn kbd{display:none}.search-btn{width:38px;justify-content:center;padding:0;border-radius:50%}
@media (max-width:1023px){.search-btn{order:1;margin-left:auto}.menu-btn{order:2!important;margin-left:0}.theme-btn{order:3!important}.site-nav{order:4!important}.brand{margin-right:0}}

/* search dialog */
.sx{width:min(680px,calc(100vw - 24px));max-height:min(640px,calc(100vh - 80px));margin:8vh auto auto;padding:0;border:1px solid var(--line);border-radius:16px;background:var(--panel);color:var(--ink);box-shadow:0 24px 60px rgba(0,0,0,.25)}
.sx::backdrop{background:rgba(10,20,16,.45);backdrop-filter:blur(2px)}
.sx-box{display:flex;flex-direction:column;max-height:inherit}
.sx-form{display:flex;align-items:center;gap:10px;padding:12px 14px;border-bottom:1px solid var(--line)}
.sx-form .i{color:var(--muted)}
.sx-form input{flex:1;min-width:0;border:0;background:none;color:var(--ink);font:500 1.1rem var(--f-body);padding:6px 0;outline:none}
.sx-form input::-webkit-search-cancel-button{display:none}
.sx-close{font:600 .72rem var(--f-mono);border:1px solid var(--line);border-radius:6px;background:var(--paper);color:var(--muted);padding:4px 8px;cursor:pointer}
.sx-body{overflow:auto;padding:6px}
.sx-list{list-style:none;margin:0;padding:0}
.sx-item{display:flex;gap:12px;align-items:flex-start;padding:10px 12px;border-radius:10px;cursor:pointer}
.sx-item[aria-selected="true"]{background:var(--copper-soft);box-shadow:inset 3px 0 0 var(--copper)}
.sx-main{display:flex;flex-direction:column;min-width:0}
.sx-main b,.search-results b{font-size:1rem}
.sx-ctx{font:600 .74rem var(--f-mono);color:var(--muted)}
.sx-snip{font-size:.88rem;color:var(--muted);overflow:hidden;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical}
.sx mark,.search-results mark{background:color-mix(in srgb,var(--glow) 40%,transparent);color:inherit;border-radius:3px;padding:0 1px}
.sx-kind{flex:none;width:82px;font:600 .66rem/1.9 var(--f-mono);letter-spacing:.06em;text-transform:uppercase;text-align:center;border-radius:6px;background:var(--paper);border:1px solid var(--line);color:var(--muted)}
.sx-kind.k-page{color:var(--copper)}.sx-kind.k-lesson{color:var(--ok)}.sx-kind.k-gloss{color:var(--violet)}.sx-kind.k-comp{color:var(--signal)}.sx-kind.k-sheet{color:var(--caution)}
.sx-empty{padding:14px 12px;color:var(--muted)}
.sx-empty p{margin:0 0 10px}
.sx-sugs{display:flex;flex-wrap:wrap;gap:6px}
.sx-sug{font:600 .85rem var(--f-body);border:1.5px solid var(--line);background:var(--paper);color:var(--ink);border-radius:999px;padding:5px 12px;cursor:pointer}
.sx-sug:hover{border-color:var(--copper)}
.sx-foot{display:flex;justify-content:space-between;gap:10px;flex-wrap:wrap;margin:0;padding:10px 14px;border-top:1px solid var(--line);font-size:.8rem;color:var(--muted)}
@media (max-width:600px){.sx{margin:0;width:100vw;max-width:100vw;height:100dvh;max-height:100dvh;border-radius:0}.sx-kind{width:auto;padding:0 6px}.sx-foot span{display:none}}

/* search page */
.search-page-form{display:flex;gap:8px;max-width:680px}
.search-page-form input{flex:1;min-width:0;font:500 1.05rem var(--f-body);padding:10px 12px;border:1.5px solid var(--line);border-radius:10px;background:var(--panel);color:var(--ink)}
.search-results{list-style:none;margin:12px 0 0;padding:0;display:grid;gap:8px;max-width:820px}
.search-results a{display:grid;grid-template-columns:90px minmax(0,1fr);gap:2px 12px;padding:12px 14px;background:var(--panel);border:1px solid var(--line);border-radius:12px;color:var(--ink);text-decoration:none}
.search-results a:hover{border-color:var(--copper)}
.search-results .sx-kind{grid-row:span 3;width:auto;align-self:start}
@media (max-width:560px){.search-results a{grid-template-columns:minmax(0,1fr)}.search-results .sx-kind{grid-row:auto;justify-self:start;padding:0 6px}}

/* glossary page */
.gl-tools{display:flex;flex-wrap:wrap;gap:10px 24px;align-items:flex-end}
.gl-tools .field{flex:1 1 280px;max-width:420px;margin:0}
.gl-tools input[type="search"]{width:100%;font:500 1rem var(--f-body);padding:9px 12px;border:1.5px solid var(--line);border-radius:10px;background:var(--panel);color:var(--ink)}
.gl-tools .status{flex-basis:100%;margin:0}
.gl-az{display:flex;flex-wrap:wrap;gap:4px;margin:18px 0 6px;position:sticky;top:64px;z-index:5;background:var(--paper);padding:8px 0;border-bottom:1px solid var(--line)}
.gl-az a{min-width:32px;text-align:center;font:700 .9rem var(--f-mono);padding:4px 6px;border-radius:7px;color:var(--ink);text-decoration:none}
.gl-az a:hover{background:var(--copper-soft)}
@media (max-width:1023px){.gl-az{top:0}}
.gl-letter{scroll-margin-top:130px}
.gl-l{font:700 1.6rem var(--f-display);color:var(--violet);margin:22px 0 6px;padding-bottom:4px;border-bottom:2px solid var(--line)}
.gl-letter dl{margin:0;display:grid;grid-template-columns:repeat(auto-fill,minmax(min(100%,360px),1fr));gap:10px}
.gl-entry{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:12px 14px;scroll-margin-top:130px}
.gl-entry.target{border-color:var(--violet);box-shadow:0 0 0 3px color-mix(in srgb,var(--violet) 25%,transparent)}
.gl-entry dt{font-weight:700;font-size:1.05rem}
.gl-entry dd{margin:4px 0 0}
.gl-entry dd p{margin:0 0 6px}
.gl-more{font-size:.86rem;color:var(--muted)}
.gl-unit{font:600 .72rem var(--f-mono);color:var(--muted);border:1px solid var(--line);border-radius:999px;padding:0 6px;margin-left:4px;vertical-align:2px}

/* glossary terms in lessons */
a.gl-term{color:inherit;text-decoration:underline dotted color-mix(in srgb,var(--violet) 70%,transparent);text-decoration-thickness:1.5px;text-underline-offset:3px;cursor:help}
a.gl-term:hover,a.gl-term:focus-visible{text-decoration-style:solid;color:var(--violet)}
.gl-tip{position:absolute;z-index:70;background:var(--panel);color:var(--ink);border:1px solid var(--line);border-top:3px solid var(--violet);border-radius:10px;box-shadow:0 12px 30px rgba(0,0,0,.18);padding:10px 12px;font-size:.9rem;line-height:1.45}
.gl-tip b{font-size:.95rem}
.gl-tip span:not(.gl-unit){display:block;margin:4px 0 6px}
.gl-tip a{font-size:.82rem;font-weight:700}
@media print{.search-btn,.gl-tip{display:none!important}a.gl-term{text-decoration:none}}
@media (max-width:389px){.brand{white-space:normal}.brand span{font-size:.9rem;line-height:1.1;max-width:calc(100vw - 232px)}}

/* ---------- v4.2: schematic view ---------- */
.sv-wrap{background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:14px;overflow-x:auto;margin-top:10px}
#sv-svg{display:block;height:auto;max-width:none;min-width:280px}
.sv-w{fill:none;stroke:var(--ink);stroke-width:2;stroke-linecap:round;stroke-linejoin:round}
.sv-thin{stroke-width:1.5}
.sv-plate{stroke-width:3}
.sv-fill{fill:var(--panel)}
.sv-dot{fill:var(--ink)}
.sv-arrow{fill:var(--ink)}
.sv-bus{stroke:var(--ink);stroke-width:2.4;stroke-linecap:round}
.sv-bus-hit{stroke:transparent;stroke-width:16;cursor:pointer}
.sv-plus .sv-bus{stroke:#D63A2F}
.sv-minus .sv-bus{stroke:#2F6FDB}
.sv-net:hover .sv-bus{stroke:var(--copper);stroke-width:4}
.sv-loose .sv-bus{stroke:var(--caution);stroke-dasharray:6 4}
.sv-open{fill:var(--panel);stroke:var(--caution);stroke-width:2}
.sv-nv{fill:var(--copper);font:700 11px var(--f-mono);paint-order:stroke;stroke:var(--panel);stroke-width:4px;stroke-linejoin:round}
.sv-name{fill:var(--ink);font:700 11px var(--f-mono);paint-order:stroke;stroke:var(--panel);stroke-width:3px;stroke-linejoin:round}
.sv-val{fill:var(--muted);font:500 10.5px var(--f-mono);paint-order:stroke;stroke:var(--panel);stroke-width:3px;stroke-linejoin:round}
.sv-pol{fill:var(--live);font:700 12px var(--f-mono)}
.sv-tiny,.sv-pin{fill:var(--muted);font:600 9px var(--f-mono)}
.sv-ic-l{fill:var(--ink);font:700 12px var(--f-mono)}
.sv-unused{stroke:var(--muted);opacity:.6}
.sv-warn{fill:var(--caution);font:700 10px var(--f-mono)}
.sv-part{cursor:pointer}
.sv-hit{fill:transparent}
.sv-part:hover .sv-w{stroke:var(--signal)}
.sv-sel .sv-w{stroke:var(--signal)}
.sv-sel .sv-name{fill:var(--signal)}
.sv-shorted .sv-w{stroke:var(--caution)}
@media (max-width:600px){#sv-svg{min-width:540px}.sv-wrap{padding:10px}}
/* ---------- v4.3: filters ---------- */
.fl-charts{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:18px;margin-top:14px}
.fl-charts h3{margin:0 0 6px;font-size:1rem}
.fl-explain{font-size:.95rem}
@media (max-width:860px){.fl-charts{grid-template-columns:minmax(0,1fr)}}
#fl-fc{white-space:normal;overflow-wrap:anywhere}
/* v4.4 power supplies */
.pw-bar{display:flex;height:14px;border-radius:7px;overflow:hidden;background:var(--line);margin:12px 0 4px}
.pw-bar span{display:block;height:100%;transition:width .2s}
.pw-load{background:var(--ok)}.pw-heat{background:var(--live)}
@media (prefers-reduced-motion:reduce){.pw-bar span{transition:none}}
.pw-chip{fill:var(--paper)}.pw-hot{fill:var(--danger-soft);stroke:var(--live)}
.pw-buck{font-size:.92rem;color:var(--muted)}
/* v4.5 motors */
.mt-switches{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:8px}
.mt-switches .btn{justify-content:flex-start;flex-direction:column;align-items:flex-start;gap:2px;text-align:left}
.mt-switches .btn span{font-size:.78rem;font-weight:400;color:var(--muted)}
.mt-switches .btn[aria-pressed="true"]{border-color:var(--signal);background:var(--ok-soft)}
.mt-sw{cursor:pointer}
.oa-w.mt-live{stroke:var(--signal);stroke-width:3.5}
.oa-w.mt-short{stroke:var(--live);stroke-width:4}
.mt-motor{fill:var(--paper)}.mt-motor.mt-on{fill:var(--ok-soft)}
.mt-arrow{stroke:var(--signal)}.mt-arrow-head{fill:var(--signal)}
.mt-explain{font-size:.95rem}
/* v4.6 buses */
.ba-controls{margin:12px 0}
.ba-panel:not([hidden]){display:flex;flex-wrap:wrap;gap:12px 18px;align-items:flex-end}
.ba-panel .field{margin:0;min-width:180px}
.ba-panel .field:first-child{flex:1 1 280px}
.ba-scope{background:var(--paper);border:1px solid var(--line);border-radius:12px;padding:12px}
.ba-scroll{overflow-x:auto;padding-bottom:6px}
.ba-scroll:focus-visible{outline:3px solid var(--focus,var(--signal));outline-offset:2px}
#ba-svg{display:block;max-width:none}
.ba-wave{fill:none;stroke:var(--ink);stroke-width:2;stroke-linecap:square}
.ba-z,.ba-zedge{fill:none;stroke:var(--muted);stroke-width:2;stroke-dasharray:4 4}
.ba-sample{stroke:var(--muted);stroke-width:1;stroke-dasharray:2 3;opacity:.7}
.ba-tick{stroke:var(--muted)}
.ba-name{fill:var(--ink);font:700 12px var(--f-mono)}
.ba-time{fill:var(--muted);font:500 10px var(--f-mono)}
.ba-bit rect,.ba-byte rect{stroke-width:1}
.ba-bit text,.ba-byte text{font:600 10px var(--f-mono);fill:var(--ink)}
.ba-ctl rect{fill:var(--ok-soft);stroke:var(--signal)}
.ba-per rect{fill:var(--copper-soft);stroke:var(--copper)}
.ba-k-start rect,.ba-k-stop rect{fill:var(--paper)}
.ba-k-ack rect{stroke-width:2}.ba-k-nack rect{fill:var(--danger-soft);stroke:var(--live)}
.ba-key-z{display:inline-block;width:16px;height:0;border-top:2px dashed var(--muted);vertical-align:middle;background:none!important}
.ba-hint{color:var(--muted);font-size:.85rem}
.ba-h3{font-size:1rem;margin:14px 0 6px}
.ba-decoded{font-family:var(--f-mono);font-size:.9rem;margin:0;padding-left:1.4em}
.ba-timing{color:var(--muted);font-size:.92rem}
@media (max-width:600px){.ba-panel .field{min-width:0;flex:1 1 100%}.ba-hint{display:block;margin-top:4px}}
.field input[type=text]{width:100%;font:1rem var(--f-body);padding:7px 10px;border:1px solid var(--line);border-radius:8px;background:var(--paper);color:var(--ink)}
.field input[type=text]:disabled{opacity:.6}
#ba-text{font-family:var(--f-mono);font-weight:600}
/* v4.7 soldering */
.sd-steps{margin:0;padding-left:1.4em;max-width:62ch}.sd-steps li{margin:0 0 8px}
.sd-joint{display:block;width:100%;max-width:340px;background:#F4F1EA;border-radius:10px}
.sd-pcb{fill:#2F6B4A}.sd-pad{fill:#C9772E}.sd-hole{fill:#1D3B2B}.sd-lead{fill:#8E979E}
.sd-solder{fill:#C4CCD3;stroke:#7C868E;stroke-width:1}.sd-solder.sd-dull{fill:#9DA3A6;stroke:#6A7175;stroke-dasharray:2 2}
.sd-shine{fill:none;stroke:#FFFFFF;stroke-width:3;stroke-linecap:round;opacity:.85}
.sd-crack{stroke:#1D1D1D;stroke-width:1.5}
.sd-cap{font:600 11px var(--f-mono);fill:#2A2A2A}
.sd-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(300px,1fr));gap:14px}
.sd-card{border:1px solid var(--line);border-radius:12px;background:var(--panel);padding:12px;margin:0;min-width:0}
.sd-card legend{font:600 .85rem var(--f-display);padding:0 6px}
.sd-card.sd-right{border-color:var(--ok)}.sd-card.sd-wrong{border-color:var(--caution)}
.sd-opts{display:grid;grid-template-columns:repeat(auto-fill,minmax(140px,1fr));gap:4px 10px;margin-top:10px;font-size:.9rem}
.sd-opts label{display:flex;gap:6px;align-items:flex-start;cursor:pointer}
.sd-opts input{margin-top:3px}
.sd-fb{font-size:.9rem;margin:10px 0 0}.sd-fb:empty{display:none}
.sd-score{font-weight:700}
/* v4.7 high contrast: independent of light and dark (footer toggle, or the system's "more contrast" setting) */
:root[data-contrast="high"]{
  --paper:#FFFFFF; --panel:#FFFFFF; --ink:#000000; --muted:#262626; --line:#4A4A4A; --grid:transparent;
  --copper:#8A3500; --copper-soft:rgba(138,53,0,.10); --on-copper:#FFFFFF;
  --signal:#0036A3; --live:#A3000B; --ok:#00552A; --glow:#FFB31F; --lo:#5A5A5A;
  --lcd-bg:#FFFFFF; --lcd-fg:#000000;
  --scope-bg:#000000; --scope-grid:rgba(255,255,255,.3); --scope-trace:#FFD60A; --scope-text:#FFFFFF;
  --caution:#6B3E00; --violet:#4B2DA8; --ok-soft:rgba(0,85,42,.10); --caution-soft:rgba(107,62,0,.10); --danger-soft:rgba(163,0,11,.09); --code-bg:#F2F2F2;
}
:root[data-contrast="high"][data-theme="dark"]{
  --paper:#000000; --panel:#000000; --ink:#FFFFFF; --muted:#E6E6E6; --line:#BDBDBD; --grid:transparent;
  --copper:#FFB27A; --copper-soft:rgba(255,178,122,.16); --on-copper:#000000;
  --signal:#9EC1FF; --live:#FF9C94; --ok:#7DF2B4; --glow:#FFD166; --lo:#8C8C8C;
  --lcd-bg:#000000; --lcd-fg:#FFFFFF;
  --scope-bg:#000000; --scope-grid:rgba(255,255,255,.3); --scope-trace:#FFE14D; --scope-text:#FFFFFF;
  --caution:#FFD27A; --violet:#C9B8FF; --ok-soft:rgba(125,242,180,.16); --caution-soft:rgba(255,210,122,.16); --danger-soft:rgba(255,156,148,.16); --code-bg:#111111;
}
@media (prefers-color-scheme: dark){
  :root[data-contrast="high"]:not([data-theme="light"]){
    --paper:#000000; --panel:#000000; --ink:#FFFFFF; --muted:#E6E6E6; --line:#BDBDBD; --grid:transparent;
    --copper:#FFB27A; --copper-soft:rgba(255,178,122,.16); --on-copper:#000000;
    --signal:#9EC1FF; --live:#FF9C94; --ok:#7DF2B4; --glow:#FFD166; --lo:#8C8C8C;
    --lcd-bg:#000000; --lcd-fg:#FFFFFF;
    --scope-bg:#000000; --scope-grid:rgba(255,255,255,.3); --scope-trace:#FFE14D; --scope-text:#FFFFFF;
    --caution:#FFD27A; --violet:#C9B8FF; --ok-soft:rgba(125,242,180,.16); --caution-soft:rgba(255,210,122,.16); --danger-soft:rgba(255,156,148,.16); --code-bg:#111111;
  }
}
:root[data-contrast="high"] :focus-visible{outline:3.5px solid var(--ink);outline-offset:3px}
:root[data-contrast="high"] main :is(p,li,td,dd) a:not([class]),:root[data-contrast="high"] .site-foot a:not(.brand){text-decoration:underline;text-underline-offset:2px}
:root[data-contrast="high"] .meter,:root[data-contrast="high"] .lab,:root[data-contrast="high"] .sd-card{border:1px solid var(--line)}
.link-btn{background:none;border:0;padding:0;font:inherit;color:inherit;text-decoration:underline;text-underline-offset:2px;cursor:pointer}
.link-btn[aria-pressed="true"]::after{content:" (on)"}