/* ee.css — reading themes + layout of the Industrial Electronics site (shared with the Electrical Engineering site EE_Web) */
:root{
  --bg:#f4f6f8; --panel:#ffffff; --panel2:#eef2f7; --ink:#202b38; --muted:#4a5a70; --line:#cfd8e3;
  --accent:#0b6fb8; --accent2:#c2356f; --good:#1d8a4a; --warn:#a9711a; --bad:#c0392b; --purple:#6f42c1;
  --chip:#e7eef6; --code:#eef2f7; --shadow:0 2px 10px rgba(20,30,50,.08);
}
:root[data-theme=warm]{ --bg:#f5efdf; --panel:#fffbef; --panel2:#f3ecd8; --ink:#332d23; --muted:#5d5140; --line:#d9ccae;
  --accent:#9a5b00; --accent2:#b23a5a; --good:#3f7d2b; --warn:#9b6a12; --bad:#b53a2c; --purple:#7a4fa6; --chip:#efe6cf; --code:#f3ecd8; }
:root[data-theme=blue]{ --bg:#e9f1f8; --panel:#f6faff; --panel2:#e3edf7; --ink:#1c3047; --muted:#3e536b; --line:#c3d3e4;
  --accent:#1963a6; --accent2:#b23a6e; --good:#25804b; --warn:#a2691a; --bad:#b9382b; --purple:#5f4bb6; --chip:#dde9f5; --code:#e3edf7; }
:root[data-theme=dark]{ --bg:#141b26; --panel:#202b3b; --panel2:#182230; --ink:#f3f6fa; --muted:#b6c2d3; --line:#3a4a63;
  --accent:#5ad1ff; --accent2:#ff7eb6; --good:#7ee787; --warn:#ffd166; --bad:#ff6b6b; --purple:#c792ea; --chip:#2a3a52; --code:#121a26; --shadow:0 2px 12px rgba(0,0,0,.35); }

*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:var(--bg);color:var(--ink);font-family:"IBM Plex Sans Thai",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;line-height:1.72;font-size:17px}
.wrap{max-width:1320px;margin:0 auto;padding:16px 18px 60px}
a{color:var(--accent)}
code,pre,.mono{font-family:"IBM Plex Mono",ui-monospace,Menlo,monospace}
code{background:var(--code);padding:1px 5px;border-radius:5px;font-size:.92em}
h1{font-size:29px;line-height:1.3;margin:10px 0 6px;font-weight:700}
h1 .en{display:block;font-size:15.5px;font-weight:500;color:var(--muted);letter-spacing:.02em}
h2{font-size:20px;margin:26px 0 8px}
h3{font-size:18px;margin:18px 0 6px}
p{margin:8px 0}
.sub{color:var(--ink);max-width:1040px}
.sub b,.notes b{color:var(--ink)}
/* ---- language blocks: static content carries data-l="th" / data-l="en" ---- */
html[data-lang="en"] [data-l="th"]{display:none !important}
html[data-lang="th"] [data-l="en"]{display:none !important}
.langsw{display:inline-flex;border:1px solid var(--line);border-radius:8px;overflow:hidden;background:var(--panel)}
.langsw button{font:inherit;font-size:14px;padding:4px 9px;border:0;background:transparent;color:var(--muted);cursor:pointer}
.langsw button.on{background:var(--accent);color:#fff;font-weight:600}
:root[data-theme=dark] .langsw button.on{color:#06202b}
/* ---- top bar ---- */
.topbar{display:flex;align-items:center;gap:12px;flex-wrap:wrap;font-size:15.5px;padding:8px 0 4px;border-bottom:1px solid var(--line);margin-bottom:8px}
.topbar .hub{font-weight:600;text-decoration:none;border:1px solid var(--line);border-radius:8px;padding:5px 10px;background:var(--panel)}
.topbar .hub:hover{border-color:var(--accent)}
.topbar .crumb{color:var(--muted)}
.topbar .visits{color:var(--muted);font-size:14px;white-space:nowrap;cursor:help}
.topbar .spacer{flex:1}
.topbar .theme{color:var(--muted);font-size:15px}
.topbar select{font:inherit;color:var(--ink);background:var(--panel);border:1px solid var(--line);border-radius:7px;padding:3px 6px;margin-left:4px}
/* ---- equation box ---- */
.equation-box{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:10px 18px 6px;margin:8px 0 14px;text-align:center;overflow-x:auto;box-shadow:var(--shadow)}
.equation-box .label{font-size:14px;color:var(--muted);letter-spacing:.02em;text-align:left;margin-bottom:2px}
.equation-box .numeric{font-size:15px;color:var(--muted);margin:-2px 0 8px}
.katex{color:var(--ink);max-width:100%}
.katex-display{overflow-x:auto;overflow-y:hidden;margin:8px 0}
.equation-box .katex{font-size:1.04em}
/* a box of several short formulas ($$…$$ $$…$$): one line when there is room, wrapped on a phone. The 2 px pad holds the 2 px sliver KaTeX
   leaves after a final subscript (.vlist-s), which would make a shrink-wrapped formula scroll sideways */
.equation-box.eqwrap{display:flex;flex-wrap:wrap;justify-content:center;column-gap:2em}
.eqwrap .katex-display{padding:0 2px}
/* ---- layout ---- */
.layout{display:grid;grid-template-columns:minmax(0,1fr) 330px;gap:14px;align-items:start;margin-top:10px}
@media (max-width:1000px){.layout{grid-template-columns:minmax(0,1fr)}}
.card{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:12px;box-shadow:var(--shadow)}
.canvas-card{padding:6px;overflow-x:auto}
.canvas-card canvas{display:block;max-width:100%;touch-action:pan-y;border-radius:8px}
.panel{padding:10px 12px;position:sticky;top:8px;max-height:calc(100vh - 16px);overflow:auto}
.panel h2{font-size:13.5px;text-transform:uppercase;letter-spacing:.06em;color:var(--muted);margin:12px 0 6px}
.panel h2:first-child{margin-top:2px}
.row{display:flex;justify-content:space-between;align-items:center;gap:6px;margin:6px 0 2px}
.row label{font-size:14.5px}
.row .val{font-family:"IBM Plex Mono",monospace;font-variant-numeric:tabular-nums;color:var(--accent);font-size:14px;min-width:52px;text-align:right}
input[type=range]{width:100%;accent-color:var(--accent);height:16px;margin:0}
.slider-block{margin:3px 0 8px}
.status{border-radius:9px;padding:8px 10px;font-size:14.5px;margin:4px 0 8px;background:var(--panel2);border:1px solid var(--line);line-height:1.5}
.pill{display:inline-block;padding:1px 8px;border-radius:999px;font-size:13px;font-weight:700;background:var(--chip);color:var(--accent);margin-right:4px}
.pill.good{color:var(--good)} .pill.bad{color:var(--bad)} .pill.warn{color:var(--warn)} .pill.purple{color:var(--purple)}
.metrics{font-size:14px;color:var(--muted);line-height:1.75;font-variant-numeric:tabular-nums;overflow-wrap:anywhere}
.metrics code{color:var(--ink)}
.metrics .kv{display:flex;justify-content:space-between;gap:8px;border-bottom:1px dashed var(--line)}
.metrics .kv:last-child{border-bottom:0}
.metrics .k{white-space:nowrap}
.toggles{display:flex;flex-wrap:wrap;gap:6px;margin:4px 0}
.btn{cursor:pointer;user-select:none;font:inherit;font-size:14px;padding:5px 9px;border-radius:7px;border:1px solid var(--line);background:var(--panel2);color:var(--ink)}
.btn:hover{border-color:var(--accent)}
.btn.on{background:var(--accent);color:#fff;border-color:var(--accent);font-weight:600}
:root[data-theme=dark] .btn.on{color:#06202b}
.btn.danger.on{background:var(--bad);border-color:var(--bad);color:#fff}
.hint{font-size:14px;color:var(--muted);margin-top:10px;line-height:1.5}
.legend{display:flex;gap:14px;font-size:14.5px;color:var(--muted);margin-top:10px;flex-wrap:wrap}
.swatch{display:inline-block;width:14px;height:3px;border-radius:2px;vertical-align:middle;margin-right:5px}
/* ---- notes / try this ---- */
.notes{margin-top:18px;display:grid;grid-template-columns:repeat(auto-fit,minmax(300px,1fr));gap:14px}
.notes .card h3{margin-top:0;font-size:16.5px}
.notes ol,.notes ul{padding-left:20px;margin:6px 0}
.notes li{margin:8px 0;line-height:1.7}
.book{font-size:14.5px;color:var(--muted);border-left:3px solid var(--purple);padding:6px 10px;background:var(--panel2);border-radius:0 8px 8px 0;margin-top:12px}
.callout{border-left:3px solid var(--accent2);padding:8px 12px;background:var(--panel2);border-radius:0 8px 8px 0;margin:12px 0;font-size:15.5px}
/* ---- prev/next ---- */
.navbar{display:flex;justify-content:space-between;gap:12px;margin-top:26px;flex-wrap:wrap}
.navlink{text-decoration:none;border:1px solid var(--line);border-radius:10px;padding:8px 14px;background:var(--panel);font-size:15.5px;max-width:48%}
.navlink:hover{border-color:var(--accent)}
.navlink.next{margin-left:auto;text-align:right}
/* ---- tables ---- */
table.tbl{border-collapse:collapse;width:100%;font-size:15.5px;background:var(--panel)}
table.tbl th,table.tbl td{border:1px solid var(--line);padding:6px 9px;vertical-align:top;text-align:left}
table.tbl th{background:var(--panel2)}
/* a wide summary table (.stack) becomes one block per row on phones, each cell led by its column name (data-h) */
@media (max-width:560px){table.tbl.stack thead{display:none}table.tbl.stack,table.tbl.stack tbody,table.tbl.stack tr,table.tbl.stack td{display:block;width:auto}table.tbl.stack tr{border:1px solid var(--line);border-top:0;padding:7px 10px}table.tbl.stack tr:first-child{border-top:1px solid var(--line)}table.tbl.stack td{border:0;padding:2px 0}table.tbl.stack td:first-child{font-weight:700}table.tbl.stack td[data-h]::before{content:attr(data-h) ': ';color:var(--muted);font-size:13.5px}}
/* ---- roadmap page ---- */
.kicker{text-transform:uppercase;letter-spacing:.16em;font-size:14px;color:var(--accent);font-weight:700;margin:16px 0 6px}
.lede{color:var(--muted);font-size:18px;max-width:860px;margin:0}
.meta{display:flex;flex-wrap:wrap;gap:8px 22px;margin:16px 0 0;font-size:15.5px;color:var(--muted)}
.meta b{color:var(--ink)}
.progress{margin:16px 0 0;background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:12px 16px;box-shadow:var(--shadow)}
.progress .prow{display:flex;align-items:center;justify-content:space-between;gap:12px;flex-wrap:wrap;font-size:15.5px;color:var(--muted)}
.progress .prow b{color:var(--ink)}
.progress .bar{height:8px;border-radius:999px;background:var(--panel2);border:1px solid var(--line);margin-top:8px;overflow:hidden}
.progress .fill{height:100%;width:0;background:linear-gradient(90deg,var(--accent),var(--good));transition:width .4s ease}
.progress button{font:inherit;background:none;border:1px solid var(--line);color:var(--muted);border-radius:999px;padding:3px 10px;font-size:14px;cursor:pointer}
.howto{margin:18px 0 8px;padding:10px 16px;border-left:3px solid var(--accent2);background:var(--panel2);border-radius:0 10px 10px 0;font-size:16px}
.legend-road{display:flex;flex-wrap:wrap;gap:8px 16px;margin:12px 0 0;font-size:14.5px;color:var(--muted);align-items:center}
.legend-road .sw{display:inline-block;width:10px;height:10px;border-radius:50%;margin-right:6px;vertical-align:middle}
.road{position:relative;margin:30px 0 0;padding-left:64px}
.road::before{content:"";position:absolute;left:23px;top:8px;bottom:8px;width:4px;border-radius:2px;background:linear-gradient(180deg,var(--accent) 0%,var(--accent2) 55%,var(--good) 100%);opacity:.5}
.milestone{position:relative;margin:36px 0 14px}
.milestone:first-child{margin-top:0}
.milestone .pin{position:absolute;left:-64px;top:2px;width:50px;height:50px;border-radius:14px;display:flex;align-items:center;justify-content:center;background:var(--panel);border:2px solid var(--accent);color:var(--accent);font-weight:800;font-size:18px;box-shadow:0 0 0 6px var(--bg)}
.milestone.s2 .pin{border-color:var(--accent2);color:var(--accent2)}
.milestone h2{font-size:23px;margin:0;padding-top:10px}
.milestone p{margin:4px 0 0;color:var(--muted);font-size:16px;max-width:800px}
.node{position:relative;margin:0 0 14px}
.node .dot{position:absolute;left:-52px;top:22px;width:28px;height:28px;border-radius:50%;background:var(--bg);border:3px solid var(--accent);display:flex;align-items:center;justify-content:center;font-size:14px;font-weight:800;color:var(--ink);box-shadow:0 0 0 5px var(--bg)}
.node.s2 .dot{border-color:var(--accent2)}
.node.read .dot{border-radius:7px;border-color:var(--purple)}
.node.cap .dot{border-color:var(--warn)}
.node.visited .dot{background:var(--good);border-color:var(--good);color:#fff}
.node.visited .dot span{display:none}
.node.visited .dot::after{content:"✓"}
a.stop{display:block;text-decoration:none;color:inherit;background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:14px 18px 12px;transition:transform .14s ease,border-color .14s ease;position:relative;box-shadow:var(--shadow)}
a.stop:hover{transform:translateX(4px);border-color:var(--accent)}
.stop .head{display:flex;align-items:center;gap:10px;flex-wrap:wrap}
.stop .step{font-size:14px;font-weight:800;letter-spacing:.06em;color:var(--accent);text-transform:uppercase}
.node.s2 .step{color:var(--accent2)}
.stop .type{font-size:13px;font-weight:700;letter-spacing:.05em;border-radius:999px;padding:1px 8px;border:1px solid var(--line);color:var(--muted)}
.stop .type.read{color:var(--purple)} .stop .type.sim{color:var(--accent)} .stop .type.cap{color:var(--warn)}
.stop h3{margin:6px 0 2px;font-size:19px}
.stop h3 .en{display:block;font-size:14px;font-weight:500;color:var(--muted)}
.stop p{margin:4px 0 0;color:var(--muted);font-size:15.5px}
.stop .goal{margin-top:8px;font-size:15px} .stop .goal b{color:var(--good)}
.stop .topics{margin-top:6px;font-size:14px;color:var(--muted)}
.stop .topics b{color:var(--purple);font-weight:600}
.tags{margin-top:8px;display:flex;flex-wrap:wrap;gap:6px}
.tag{font-size:13.5px;color:var(--accent);background:var(--chip);border:1px solid var(--line);border-radius:999px;padding:1px 9px}
.stop .katex{font-size:1.1em;color:inherit}   /* roadmap cards: math in the colour of its own text, sized to sit with the Thai font */
.arrow{position:absolute;top:14px;right:16px;color:var(--muted);font-size:21px}
footer{margin-top:44px;border-top:1px solid var(--line);padding-top:16px;color:var(--muted);font-size:15px}
/* ---- phone ---- */
@media (max-width:640px){
  .wrap{padding:12px 16px 50px} h1{font-size:23px}
  .road{padding-left:44px} .road::before{left:14px}
  .milestone .pin{left:-44px;width:34px;height:34px;border-radius:10px;font-size:15.5px}
  .node .dot{left:-40px;top:18px;width:24px;height:24px;font-size:13px}
  .panel{position:static;max-height:none}
  .equation-box .katex{font-size:.9em}
  .navlink{max-width:100%}
}
@media (pointer:coarse){ .btn{padding:8px 12px;min-height:34px} input[type=range]{height:26px} }

/* ---- inline figures (figs.js) ---- */
.fig{margin:10px auto 6px;max-width:560px}
.fig svg{width:100%;height:auto;display:block}
.fig .cap{font-size:14px;color:var(--muted);text-align:center;margin-top:4px;line-height:1.45}
.fig.wide{max-width:820px}
/* ---- step-by-step derivation (stop 1) ---- */
details.derive{margin-top:14px}
details.derive summary{cursor:pointer;font-weight:700;font-size:16.5px;color:var(--ink)}
details.derive summary::marker{color:var(--accent)}
.derive .step{display:grid;grid-template-columns:34px minmax(0,1fr);gap:8px;align-items:start;padding:8px 0;border-top:1px dashed var(--line)}
.derive .step:first-of-type{border-top:0}
.derive .step .n{width:28px;height:28px;border-radius:50%;background:var(--chip);color:var(--accent);font-weight:700;display:flex;align-items:center;justify-content:center;font-size:14.5px}
.derive .step h4{margin:4px 0 2px;font-size:15.5px}
.derive .step p{margin:4px 0;font-size:15.5px;line-height:1.6}
.derive .step .katex-display{margin:6px 0}
.derive .two{display:grid;grid-template-columns:repeat(auto-fit,minmax(280px,1fr));gap:12px;align-items:start}
.derive img.slx{width:100%;max-width:900px;display:block;margin:6px auto;border:1px solid var(--line);border-radius:8px;background:#fff}
.derive pre.code{background:var(--code);border:1px solid var(--line);border-radius:8px;padding:10px 12px;font-size:14px;line-height:1.5;overflow-x:auto;margin:8px 0}

/* =================== EE site additions =================== */
/* ---- roadmap: planned (not yet written) stops ---- */
.node.soon .dot{border-style:dashed;border-color:var(--line);color:var(--muted)}
.node.soon .stop{opacity:.62;padding:9px 16px 8px;box-shadow:none;background:var(--panel2)}
.node.soon .stop:hover{transform:none;border-color:var(--line)}
.node.soon h3{font-size:16.5px;margin:3px 0 0}
.node.soon p{font-size:14.5px}
.stop .type.soon{color:var(--muted);border-style:dashed}
.milestone.soon .pin{border-color:var(--line);color:var(--muted);border-style:dashed}
/* ---- roadmap: the exam-review stop (stage 5, type 'rev') ---- */
.milestone.s5 .pin{border-color:var(--good);color:var(--good)}
.node.rev .dot{border-color:var(--good);color:var(--good)}
.node.s5 .step,.stop .type.rev{color:var(--good)}
/* ---- roadmap: the supplement on ac analysis (stage 6) ---- */
.milestone.s6 .pin{border-color:var(--purple);color:var(--purple)}
.node.s6 .dot{border-color:var(--purple)}
.node.s6 .step{color:var(--purple)}
.node.s6 .dot span{font-size:11px}
/* hero demo on the roadmap */
.hero{display:grid;grid-template-columns:minmax(0,1.25fr) minmax(0,1fr);gap:16px;align-items:center;margin-top:8px}
@media (max-width:860px){.hero{grid-template-columns:minmax(0,1fr)}}
.hero .card{padding:6px}
.hero canvas{display:block;max-width:100%;border-radius:8px;cursor:pointer}
.hero .cap{font-size:14px;color:var(--muted);padding:4px 6px 2px}
.keys{display:grid;grid-template-columns:auto 1fr;gap:6px 10px;font-size:15.5px;align-items:center}
.keys .k{display:flex;align-items:center;justify-content:center;min-width:38px;height:22px;padding:0 4px;border-radius:6px;background:#0f1220;white-space:nowrap}
.keys .k i{display:inline-block;width:7px;height:7px;border-radius:50%;margin:0 2px}
/* ---- equations, matrices, steppers ---- */
.eqcard{margin-top:14px}
.eqcard h3{margin:0 0 6px;font-size:18px}
.eqcard .lead{color:var(--ink);font-size:15.5px;margin:0 0 8px}
.eqgrid{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:14px}
@media (max-width:900px){.eqgrid{grid-template-columns:minmax(0,1fr)}}
.steps{margin:8px 0 0;padding:0;list-style:none;counter-reset:st}
.steps li{display:grid;grid-template-columns:30px minmax(0,1fr);gap:8px;align-items:start;padding:7px 0;border-top:1px dashed var(--line);animation:stepIn .45s ease}
.steps li:first-child{border-top:0}
.steps li::before{counter-increment:st;content:counter(st);width:24px;height:24px;border-radius:50%;background:var(--chip);color:var(--accent);font-weight:700;font-size:14px;display:flex;align-items:center;justify-content:center;margin-top:3px}
.steps li.done::before{background:var(--good);color:#fff;content:"✓"}
.steps .why{font-size:16px;color:var(--ink);font-weight:500}
.steps .katex-display{margin:4px 0;text-align:left}
.steps .katex-display>.katex{text-align:left}
@keyframes stepIn{from{opacity:0;transform:translateY(-6px)}to{opacity:1;transform:none}}
.stepbar{display:flex;flex-wrap:wrap;gap:6px;align-items:center;margin:6px 0}
.stepbar .count{font-size:14px;color:var(--muted);margin-left:auto}
.answer{border:1px solid var(--good);background:color-mix(in srgb,var(--good) 10%,var(--panel));border-radius:10px;padding:8px 12px;margin-top:8px;font-size:16px}
.warnbox{border:1px solid var(--warn);background:color-mix(in srgb,var(--warn) 10%,var(--panel));border-radius:10px;padding:8px 12px;margin-top:8px;font-size:15.5px}
.badbox{border:1px solid var(--bad);background:color-mix(in srgb,var(--bad) 9%,var(--panel));border-radius:10px;padding:8px 12px;margin-top:8px;font-size:15.5px}
/* matrix shown as an HTML table with brackets; columns can be highlighted */
.mat{display:inline-grid;position:relative;padding:4px 10px;margin:4px 2px;vertical-align:middle;font-family:"IBM Plex Mono",monospace;font-variant-numeric:tabular-nums}
.mat::before,.mat::after{content:"";position:absolute;top:0;bottom:0;width:8px;border:2px solid var(--ink)}
.mat::before{left:0;border-right:0;border-radius:4px 0 0 4px}
.mat::after{right:0;border-left:0;border-radius:0 4px 4px 0}
.mat.det::before,.mat.det::after{width:0;border-radius:0}
.mat.det::before{border-right:0}
.mat > span{padding:3px 8px;text-align:right;min-width:2.6em;border-radius:5px;transition:background .3s,color .3s}
.mat > span.hl{background:color-mix(in srgb,var(--accent2) 22%,transparent);color:var(--ink);font-weight:700}
.mat > span.hlb{background:color-mix(in srgb,var(--good) 22%,transparent);font-weight:700}
.mat > span.fly{animation:fly .6s ease}
@keyframes fly{from{transform:translateX(60px);opacity:0}to{transform:none;opacity:1}}
.matrow{display:flex;flex-wrap:wrap;align-items:center;gap:6px 10px;margin:6px 0}
.matrow .op{font-size:20px;color:var(--muted)}
.matlabel{font-size:14.5px;color:var(--muted);text-align:center}
.mi{width:4.2em;font:inherit;font-family:"IBM Plex Mono",monospace;font-size:15px;padding:3px 5px;border:1px solid var(--line);border-radius:6px;background:var(--panel);color:var(--ink);text-align:right}
.mi:focus{outline:2px solid var(--accent);outline-offset:0}
.sarrus{width:100%;max-width:520px;display:block;margin:4px 0}
.terms{font-family:"IBM Plex Mono",monospace;font-size:14.5px;line-height:1.9;overflow-wrap:anywhere}
.terms .t{padding:1px 4px;border-radius:4px;transition:background .25s}
.terms .t.on{background:color-mix(in srgb,var(--warn) 30%,transparent)}
.terms .t.p{color:var(--good)} .terms .t.m{color:var(--bad)}
/* ---- quiz ---- */
.quiz{display:grid;gap:8px;margin-top:6px}
.qrow{display:grid;grid-template-columns:minmax(150px,1.1fr) minmax(0,2fr) auto;gap:8px;align-items:center;padding:6px 0;border-top:1px dashed var(--line)}
.qrow:first-child{border-top:0}
@media (max-width:640px){.qrow{grid-template-columns:minmax(0,1fr)}}
.qrow .q{font-size:16.5px}
.qrow .ins{display:flex;flex-wrap:wrap;gap:6px;align-items:center;font-size:15px;color:var(--muted)}
.qrow input{width:6.2em;font:inherit;font-family:"IBM Plex Mono",monospace;font-size:15px;padding:4px 6px;border:1px solid var(--line);border-radius:6px;background:var(--panel);color:var(--ink)}
.qrow input.ok{border-color:var(--good);background:color-mix(in srgb,var(--good) 12%,var(--panel))}
.qrow input.no{border-color:var(--bad);background:color-mix(in srgb,var(--bad) 10%,var(--panel))}
.qrow .res{font-size:14.5px;min-width:6em}
.qrow details{grid-column:1/-1;font-size:15px;color:var(--muted)}
.qrow details summary{cursor:pointer;color:var(--accent)}
.score{font-size:15px;color:var(--muted)}
.score b{color:var(--good)}
/* small inline swatches for mesh colours etc. */
.chip{display:inline-block;padding:0 7px;border-radius:999px;font-size:13.5px;font-weight:700;color:#0f1220}
.subcanvas canvas{display:block;max-width:100%;border-radius:8px}

/* ---- readability pass (Oct 2026): emphasis and key-point boxes ---- */
b,strong{font-weight:700}
.sub b,.lead b,.notes b,.keypoints b{color:var(--ink)}
.keypoints{border:1px solid color-mix(in srgb,var(--accent) 45%,var(--line));background:color-mix(in srgb,var(--accent) 7%,var(--panel));border-radius:12px;padding:10px 18px 8px;margin:14px 0 6px;box-shadow:var(--shadow)}
.keypoints h2{font-size:16px;margin:0 0 4px;color:var(--accent);letter-spacing:.02em}
.keypoints ul{margin:4px 0;padding-left:22px}
.keypoints li{margin:6px 0;line-height:1.65}
.keypoints .katex{font-size:1.05em}
/* ---- convention strip of the AC pages (course rule: sine reference; peak or rms size), filled by shell.js from data-mag ---- */
.conv{display:flex;flex-wrap:wrap;align-items:baseline;gap:4px 16px;background:var(--panel);border:1px solid var(--line);border-left:5px solid var(--accent2);border-radius:10px;padding:8px 16px;margin:10px 0 8px;box-shadow:var(--shadow);line-height:1.6}
.conv .ct{font-size:13px;font-weight:700;letter-spacing:.05em;color:var(--accent2);white-space:nowrap}
.conv .cf{font-weight:700;font-size:16.5px}
.conv .cm{font-weight:700;font-size:16px;color:var(--accent)}
.conv .cx{flex-basis:100%;font-size:15px;color:var(--muted)}
.conv .cx b{color:var(--ink)}
/* ---- chapter 3: list of loops in a counting step ---- */
.looplist{margin:6px 0 2px;padding-left:30px;columns:2 210px;column-gap:26px;font-family:"IBM Plex Mono",monospace;font-size:15px;line-height:1.65}
.looplist li{break-inside:avoid}
.steps li{padding:10px 0}
.steps .katex-display{margin:6px 0 4px}
.answer .katex{font-size:1.1em}
.metrics .k{color:var(--muted)}
.metrics code{font-size:14px}

/* ---- chapter 4: analysis steps, drills ---- */
.steps .sub2,.sub2{font-size:15.5px;color:var(--muted);margin:4px 0 2px;line-height:1.55}
.steps ul.ul2{margin:4px 0 2px;padding-left:22px;list-style:disc}
.steps ul.ul2 li{display:list-item;padding:3px 0;border-top:0;animation:none;grid-template-columns:none}
.steps ul.ul2 li::before{content:none;display:none;counter-increment:none}
details.alt{margin:10px 0 2px;border:1px dashed var(--line);border-radius:8px;padding:5px 12px;background:var(--panel2)}
details.alt summary{cursor:pointer;color:var(--accent);font-weight:600;font-size:15.5px}
.drill{margin-top:6px}
.dgrid{display:inline-grid;gap:6px 6px;align-items:center;padding:6px 0}
.dgrid .dop{font-size:20px;color:var(--muted);text-align:center}
.dgrid .dvar{min-width:2.2em;text-align:center}
.dgrid input.ok{border-color:var(--good);background:color-mix(in srgb,var(--good) 12%,var(--panel))}
.dgrid input.no{border-color:var(--bad);background:color-mix(in srgb,var(--bad) 10%,var(--panel))}
.cmp{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:14px;margin-top:8px}
@media (max-width:900px){.cmp{grid-template-columns:minmax(0,1fr)}}
.cmp .card h3{margin:0 0 4px;font-size:17px}
.bars{display:grid;grid-template-columns:auto 1fr auto;gap:6px 10px;align-items:center;font-size:15.5px;margin:6px 0}
.bars .bar{height:16px;border-radius:5px;background:var(--accent)}
.bars .bar.m{background:var(--accent2)}
.win{font-weight:700;color:var(--good)}
.qrow.wide{grid-template-columns:minmax(260px,460px) minmax(0,1fr) auto}
@media (max-width:760px){.qrow.wide{grid-template-columns:minmax(0,1fr)}}
/* KaTeX's hidden MathML is position:absolute; a positioned scroll container keeps it from widening the page on phones */
.equation-box,.eqcard,.katex-display{position:relative}
.eqcard{overflow-x:auto}

/* ==== problem-by-problem pages (rebuilt from chapter 1, Oct 2026): slide pictures, one section per problem, instructor-style stepper ==== */
figure.slide{margin:10px 0 6px}
figure.slide img{display:block;width:100%;height:auto;border:1px solid var(--line);border-radius:10px;background:#fff;cursor:zoom-in;box-shadow:var(--shadow)}
:root[data-theme=dark] figure.slide img{filter:brightness(.93)}
figure.slide figcaption{font-size:14px;color:var(--muted);margin-top:4px;line-height:1.45}
figure.slide.q{max-width:720px}
figure.slide.q.wide{max-width:860px}
figure.slide.q.sm{max-width:430px} figure.slide.q.xs{max-width:330px}   /* small crops (chapter 3) are not blown up past their own size */
.slides{display:grid;grid-template-columns:repeat(auto-fit,minmax(300px,1fr));gap:12px;margin:8px 0}
.slides figure.slide{margin:0}
/* ---- story blocks (Oct 2026): every slide sits at the point of the page where its idea is used, inside a short narrative that
   leads into the simulation or problem below it (storify.py in the build notes). Desktop: text beside one slide, or text above a
   row of two to four; phones: stacked. A block before a section joins it: that section loses its top rule. ---- */
.story{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.08fr);gap:12px 24px;align-items:start;margin:46px 0 0;padding-top:16px;border-top:3px solid var(--line)}
.story.n2,.story.n3,.story.n4,.story.n0{grid-template-columns:minmax(0,1fr)}
.story.in{margin:12px 0 14px;padding-top:0;border-top:0}
@media (max-width:860px){.story{grid-template-columns:minmax(0,1fr)}}
.story-k{font-size:13px;font-weight:800;letter-spacing:.07em;text-transform:uppercase;color:var(--accent2)}
.story h2{margin:3px 0 6px;font-size:22px;line-height:1.35}
.story-p p{margin:6px 0;font-size:16.5px;line-height:1.75}
.story.in .story-p p{font-size:16px}
.story-next{grid-column:1/-1;margin:2px 0 0;font-size:15.5px;font-weight:600;color:var(--accent)}
.story-f{display:grid;gap:12px;grid-template-columns:minmax(0,1fr);min-width:0}
.story.n2 .story-f{grid-template-columns:repeat(2,minmax(0,1fr))}
.story.n3 .story-f,.story.n4 .story-f{grid-template-columns:repeat(auto-fit,minmax(230px,1fr))}
@media (max-width:640px){.story.n2 .story-f{grid-template-columns:minmax(0,1fr)}}
.story-f figure.slide{margin:0}
.story .warnbox{grid-column:1/-1;margin-top:2px}
.story + .prob{margin-top:18px;padding-top:0;border-top:0}
.lightbox{position:fixed;inset:0;z-index:1000;background:rgba(8,10,18,.9);display:none;align-items:center;justify-content:center;flex-direction:column;padding:14px;cursor:zoom-out}
.lightbox.on{display:flex}
.lightbox img{max-width:100%;max-height:calc(100% - 34px);border-radius:8px;background:#fff}
.lightbox .lbx{position:absolute;top:10px;right:12px;font:inherit;font-size:20px;line-height:1;padding:6px 11px;border-radius:8px;border:1px solid #667;background:#1b2140;color:#fff;cursor:pointer}
.lightbox .lbcap{color:#dfe5f2;font-size:14.5px;margin-top:6px}
/* one problem = one section */
.prob{margin:40px 0 0;padding-top:14px;border-top:3px solid var(--line);scroll-margin-top:8px}
.prob-head{display:flex;gap:12px;align-items:flex-start;margin-bottom:6px}
.prob-no{flex:none;min-width:46px;height:46px;padding:0 8px;border-radius:12px;background:var(--accent);color:#fff;font-weight:800;font-size:19px;display:flex;align-items:center;justify-content:center;letter-spacing:.02em}
:root[data-theme=dark] .prob-no{color:#06202b}
.prob-head h2{margin:2px 0 0;font-size:22px;line-height:1.35}
.prob-head .src{color:var(--muted);font-size:15px;margin-top:2px}
.prob .lead{font-size:16px;margin:6px 0 8px;max-width:1040px}
.prob.sub-item{margin-top:26px;border-top:1px dashed var(--line);padding-top:10px}
.prob.sub-item .prob-no{min-width:40px;height:40px;font-size:16.5px;background:var(--chip);color:var(--accent)}
.prob.sub-item .prob-head h2{font-size:19px}
.group-head{margin:46px 0 4px;padding-top:12px;border-top:3px solid var(--line)}
.group-head h2{margin:0;font-size:23px}
.given{border:1px solid var(--line);background:var(--panel2);border-radius:10px;padding:8px 14px;margin:6px 0 8px;font-size:16px;overflow-x:auto;position:relative}
.given .gl{font-size:14.5px;font-weight:700;color:var(--accent2);letter-spacing:.02em}
.given .katex-display{margin:6px 0}
.duo{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:14px;align-items:start;margin-top:10px}
.duo > .sim{position:sticky;top:8px}
.duo.wide-sim{grid-template-columns:minmax(0,1.15fr) minmax(0,1fr)}
@media (max-width:1000px){.duo,.duo.wide-sim{grid-template-columns:minmax(0,1fr)} .duo > .sim{position:static}}
.sim{padding:6px}
.sim canvas{display:block;max-width:100%;border-radius:8px;touch-action:pan-y}
.ctl{display:grid;grid-template-columns:repeat(auto-fit,minmax(128px,1fr));gap:2px 14px;padding:4px 8px 2px}
.ctl .slider-block{margin:2px 0 6px}
.simnote{font-size:14.5px;color:var(--muted);padding:2px 8px 4px;line-height:1.5}
.simnote b{color:var(--ink)}
.readout{font-size:15px;padding:4px 8px;font-variant-numeric:tabular-nums;line-height:1.7}
.readout code{font-size:14.5px}
.solve{padding:12px 14px}
.solve h3{margin:0 0 4px;font-size:17px}
/* the stepper */
.stepper{margin-top:6px}
.stepper .steps{margin:4px 0 0}
.stepper .steps li{scroll-margin-bottom:84px;scroll-margin-top:12px;border-radius:8px;padding:10px 6px 10px 0}
.stepper .steps li.noanim{animation:none}
.stepper .steps li.cur{background:color-mix(in srgb,var(--accent) 9%,transparent);box-shadow:inset 3px 0 0 var(--accent)}
.stepper .steps li.done::before{content:counter(st);background:var(--good);color:#fff}
:root[data-theme=dark] .stepper .steps li.done::before{color:#0f1a12}
.stepper .steps li::before{margin-left:4px}
.stepper .why{font-size:16.5px;line-height:1.6}
.stepper .sb{min-width:0}
.stepper .stepbar{position:sticky;bottom:6px;z-index:5;background:var(--panel);border:1px solid var(--line);border-radius:10px;padding:6px 8px;margin:8px 0 2px;box-shadow:0 -2px 12px rgba(20,30,50,.12)}
.stepper .stepbar .btn[data-a="next"]{font-size:15.5px;padding:7px 14px}
.stepper .stepbar .btn:disabled{opacity:.45;cursor:default;border-color:var(--line)}
.stepper .stepbar .count{display:flex;align-items:center;gap:8px;margin-left:auto;font-size:14px;color:var(--muted)}
.stepper .pdots{display:inline-flex;gap:3px}
.stepper .pdots i{width:8px;height:8px;border-radius:50%;background:var(--line);display:inline-block}
.stepper .pdots i.on{background:var(--good)}
.stepper .shint{font-size:15px;color:var(--muted);margin:2px 0}
.stepper .shint:empty{display:none}
.stepper .final:empty{display:none}
@media (max-width:480px){.stepper .steps .katex-display{font-size:.9em}}   /* long step formulas fit a phone without sideways scrolling */
@media (max-width:640px){.stepper .pdots{display:none} .prob-head h2{font-size:19.5px} .prob-no{min-width:40px;height:40px;font-size:17px}}
/* "try it first" answer box */
.ask{display:flex;flex-wrap:wrap;gap:6px 10px;align-items:center;font-size:15px;padding:6px 10px;border:1px dashed var(--line);border-radius:10px;margin:6px 0}
.ask .asklab{font-weight:700;color:var(--accent2)}
.ask input.ok{border-color:var(--good);background:color-mix(in srgb,var(--good) 12%,var(--panel))}
.ask input.no{border-color:var(--bad);background:color-mix(in srgb,var(--bad) 10%,var(--panel))}
.ask .askres{font-size:14.5px}
details.orig{margin:12px 0 0;border:1px solid var(--line);border-radius:10px;padding:6px 12px;background:var(--panel)}
details.orig summary{cursor:pointer;font-weight:600;color:var(--accent);font-size:15.5px}
.chips{display:flex;flex-wrap:wrap;gap:6px;margin:6px 0}
.chips .pill{font-family:"IBM Plex Mono",monospace;font-size:14.5px;padding:2px 10px}
.toc{display:flex;flex-wrap:wrap;gap:6px 8px;align-items:center;margin:16px 0 4px;font-size:15px}
.toc .tl{font-weight:700;color:var(--muted);margin-right:2px}
.toc a{text-decoration:none;border:1px solid var(--line);background:var(--panel);border-radius:999px;padding:3px 12px;color:var(--ink)}
.toc a:hover{border-color:var(--accent)}
.toc a b{color:var(--accent);margin-right:5px}
.intro-duo{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:16px;align-items:center;margin-top:8px}
@media (max-width:900px){.intro-duo{grid-template-columns:minmax(0,1fr)}}
.intro-duo .sub{margin:0}
@media (max-width:640px){.given .katex-display>.katex,.stepper .katex-display>.katex,.solve .katex-display>.katex{font-size:1.02em}}
@media (max-width:480px){.solve .katex-display{font-size:.9em}}   /* formula boxes beside the steppers (fitted by LS.fitIn) match the step formulas */
.stepper .sarrus{max-width:440px}
.duo.big-sim{grid-template-columns:minmax(0,1.65fr) minmax(0,1fr)}
@media (min-width:1001px) and (max-width:1200px){.duo.big-sim{grid-template-columns:minmax(0,1.35fr) minmax(0,1fr)}}   /* keep the solution column readable on small laptops */
@media (max-width:1000px){.duo.big-sim{grid-template-columns:minmax(0,1fr)}}
.sim.hscroll{overflow-x:auto}
.sim.hscroll canvas{max-width:none}
/* chapter 4: the nodal-vs-mesh table of page 4.4, the "by inspection" drill boxes */
table.cmptab{min-width:560px} table.cmptab td{vertical-align:middle}
details.drillbox .sub2{margin:6px 0 2px}
details.drillbox .drill{overflow-x:auto;position:relative}
.stepper .mstack .katex-display{font-size:.86em}   /* a step formula that cannot fit its column even after LS.fit (any screen) */
@media (max-width:480px){.stepper .mstack .katex-display{font-size:.8em}}   /* elimination stacks and determinants cannot wrap */
/* chapter 5: a demo's control panel inside the solve card (not sticky there), the formula and stepper of a demo below it */
.solve > .panel{position:static;max-height:none;overflow:visible;padding:0}
.solve > .panel + h3,.solve > .panel + .stepper{margin-top:12px}
/* the anonymous feedback box at the end of every page (shell.js feedbackBox, sent to the instructor's Google Form) */
.fb{margin-top:30px;background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:14px 16px;box-shadow:var(--shadow)}
.fb h2{margin:0 0 4px;font-size:18px}
.fb .fb-anon{font-size:13px;font-weight:600;color:var(--good);border:1px solid var(--line);border-radius:999px;padding:1px 9px;margin-left:6px;vertical-align:2px;white-space:nowrap}
.fb .fb-q{margin:2px 0 10px;color:var(--muted)}
.fb-rate{display:flex;flex-wrap:wrap;align-items:center;gap:8px}
.fb-rate button{min-width:44px;height:40px;border-radius:10px;border:1px solid var(--line);background:var(--chip);color:var(--ink);font:inherit;font-weight:700;cursor:pointer}
.fb-rate button.on{background:var(--accent);border-color:var(--accent);color:#fff}
.fb-ends{font-size:13.5px;color:var(--muted);margin-left:4px}
.fb-kind{display:flex;flex-wrap:wrap;gap:6px 16px;margin:12px 0 10px;font-size:15px}
.fb-kind label{display:inline-flex;align-items:center;gap:6px;cursor:pointer}
.fb textarea{display:block;width:100%;box-sizing:border-box;border:1px solid var(--line);border-radius:10px;padding:8px 10px;font:inherit;font-size:15.5px;background:var(--bg);color:var(--ink);resize:vertical}
.fb-row{display:flex;align-items:center;gap:12px;margin-top:10px;flex-wrap:wrap}
.fb-send{border:0;border-radius:10px;padding:8px 18px;background:var(--accent);color:#fff;font:inherit;font-weight:700;cursor:pointer}
.fb-send:disabled{opacity:.55;cursor:default}
.fb-msg{font-size:14.5px;color:var(--muted)}
.fb-note{margin:10px 0 0;font-size:13.5px;color:var(--muted)}
:root[data-theme=dark] .fb-rate button.on,:root[data-theme=dark] .fb-send{color:#06202b}