/* ============ CO Test 1 — style.css ============
   Look: an engineering datasheet. Paper + ink, one signal colour, hairline rules, no rounded "app cards". */
:root {
  --bg: #f3efe6;
  --paper: #faf8f2;
  --ink: #17150f;
  --ink-2: #4b4739;
  --ink-3: #8a8473;
  --rule: #d8d1bf;
  --rule-strong: #17150f;
  --tint: #ece6d8;
  --sig: #d9480f;
  --sig-ink: #b23a08;
  --sig-tint: #fbe4d6;
  --ok: #2f7d32;
  --ok-tint: #e3efd9;
  --bad: #c0262d;
  --bad-tint: #f7dcd8;
  --warn: #9a6b00;
  --warn-tint: #f5ead0;
  --t1: #1f5fa8; --t2: #7a3fa0; --t3: #1d7a6c;
  --grid: rgba(23, 21, 15, .045);
  --sans: 'IBM Plex Sans', system-ui, sans-serif;
  --serif: 'IBM Plex Serif', Georgia, serif;
  --mono: 'IBM Plex Mono', ui-monospace, Consolas, monospace;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #111110; --paper: #181816; --ink: #ece7da; --ink-2: #b9b3a4; --ink-3: #7d786c;
    --rule: #2f2e2a; --rule-strong: #ece7da; --tint: #22211e;
    --sig: #ff7a3d; --sig-ink: #ff9a6a; --sig-tint: #3a2216;
    --ok: #7cc47f; --ok-tint: #1c2a1b; --bad: #ff7b7b; --bad-tint: #341b1b; --warn: #e3b341; --warn-tint: #2f2716;
    --t1: #7fb0ea; --t2: #c49ae0; --t3: #6fd0bf; --grid: rgba(236, 231, 218, .035);
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #111110; --paper: #181816; --ink: #ece7da; --ink-2: #b9b3a4; --ink-3: #7d786c;
  --rule: #2f2e2a; --rule-strong: #ece7da; --tint: #22211e;
  --sig: #ff7a3d; --sig-ink: #ff9a6a; --sig-tint: #3a2216;
  --ok: #7cc47f; --ok-tint: #1c2a1b; --bad: #ff7b7b; --bad-tint: #341b1b; --warn: #e3b341; --warn-tint: #2f2716;
  --t1: #7fb0ea; --t2: #c49ae0; --t3: #6fd0bf; --grid: rgba(236, 231, 218, .035);
  color-scheme: dark;
}

* { box-sizing: border-box; }
html { scroll-padding-top: 80px; }
body {
  margin: 0; color: var(--ink); font: 16px/1.62 var(--sans);
  background-color: var(--bg);
  background-image: linear-gradient(var(--grid) 1px, transparent 1px), linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 24px 24px;
  -webkit-font-smoothing: antialiased;
}
::selection { background: var(--sig); color: #fff; }
a { color: var(--sig-ink); text-decoration: underline; text-decoration-thickness: 1px; text-underline-offset: 3px; }
a:hover { color: var(--sig); }
h1, h2, h3, h4 { margin: 0 0 .5em; line-height: 1.2; font-weight: 600; }
h1 { font-family: var(--serif); font-weight: 500; font-size: clamp(2rem, 4.4vw, 3.1rem); letter-spacing: -.02em; line-height: 1.08; }
h1 em { font-style: italic; color: var(--sig); }
h2 { font-size: 1.3rem; letter-spacing: -.01em; }
h3 { font-size: 1.05rem; }
h4 { font-family: var(--mono); font-size: .78rem; font-weight: 600; text-transform: uppercase; letter-spacing: .08em; color: var(--ink-2); margin-top: 1.6em; }
p { margin: 0 0 .9em; }
ul, ol { margin: 0 0 1em; padding-left: 1.3em; }
li { margin: .25em 0; }
li::marker { color: var(--ink-3); }
.mono, code, kbd { font-family: var(--mono); font-size: .92em; }
sub, sup { font-size: .72em; }
b, strong { font-weight: 600; }
.muted { color: var(--ink-3); }
.err { color: var(--bad); font-weight: 500; }
.wrap { max-width: 1160px; margin: 0 auto; padding: 0 24px; }
#app { padding-top: 34px; padding-bottom: 56px; min-height: 70vh; }
kbd { border: 1px solid var(--ink-3); border-bottom-width: 2px; padding: 0 5px; font-size: .78em; background: var(--paper); }

/* ---------- masthead ---------- */
.top { position: sticky; top: 0; z-index: 50; background: var(--paper); border-bottom: 2px solid var(--rule-strong); }
.top-in { max-width: 1160px; margin: 0 auto; padding: 0 24px; display: flex; align-items: stretch; gap: 22px; height: 58px; }
.logo { display: flex; align-items: center; gap: 10px; color: var(--ink); text-decoration: none; flex-shrink: 0; }
.logo-mark { font: 600 .82rem var(--mono); border: 1.5px solid var(--ink); padding: 3px 6px; letter-spacing: .04em; position: relative; }
.logo-mark::before, .logo-mark::after { content: ''; position: absolute; left: 4px; right: 4px; height: 4px; background: repeating-linear-gradient(90deg, var(--ink) 0 2px, transparent 2px 6px); }
.logo-mark::before { top: -6px; } .logo-mark::after { bottom: -6px; }
.logo-txt { display: flex; flex-direction: column; line-height: 1.15; }
.logo-txt b { font-size: .95rem; }
.logo-txt small { font: .7rem var(--mono); color: var(--ink-3); }
.nav { display: flex; flex: 1; overflow-x: auto; scrollbar-width: none; }
.nav::-webkit-scrollbar { display: none; }
.nav a { display: flex; align-items: center; gap: 7px; padding: 0 13px; color: var(--ink-2); font-size: .9rem; font-weight: 500; white-space: nowrap; text-decoration: none; border-bottom: 3px solid transparent; margin-bottom: -2px; }
.nav a:hover { color: var(--ink); }
.nav a.on { color: var(--ink); border-bottom-color: var(--sig); }
.nav .ic { font: .7rem var(--mono); color: var(--ink-3); }
.nav a.on .ic { color: var(--sig); }
.theme-btn { align-self: center; flex-shrink: 0; border: 1px solid var(--ink); background: transparent; color: var(--ink); cursor: pointer; font: 500 .72rem var(--mono); text-transform: uppercase; letter-spacing: .06em; padding: 5px 9px; }
.theme-btn:hover { background: var(--ink); color: var(--paper); }
.courses-btn { align-self: center; flex-shrink: 0; margin-right: -12px; border: 1px solid var(--ink); background: var(--ink); color: var(--paper); font: 500 .72rem var(--mono); text-transform: uppercase; letter-spacing: .06em; padding: 5px 9px; text-decoration: none; white-space: nowrap; }
.courses-btn:hover { background: var(--sig); border-color: var(--sig); color: #fff; }
.theme-btn .moon { display: none; }
:root[data-theme="dark"] .theme-btn .sun { display: none; }
:root[data-theme="dark"] .theme-btn .moon { display: inline; }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .theme-btn .sun { display: none; } :root:not([data-theme="light"]) .theme-btn .moon { display: inline; } }
.foot { color: var(--ink-3); font: .74rem var(--mono); padding-top: 18px; padding-bottom: 40px; border-top: 1px solid var(--rule); }
body.in-test .foot { display: none; }
.foot { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 8px 20px; }
.ig-credit { display: inline-flex; align-items: center; gap: 6px; color: var(--ink); text-decoration: none; font-weight: 500; }
.ig-credit:hover { color: var(--sig); text-decoration: underline; }

/* ---------- buttons & labels ---------- */
.btn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; padding: 10px 18px; border: 1.5px solid var(--ink); background: transparent; color: var(--ink); font: 500 .9rem var(--sans); cursor: pointer; text-decoration: none; transition: background .12s, color .12s; }
.btn:hover { background: var(--ink); color: var(--paper); }
.btn:disabled { opacity: .35; cursor: not-allowed; background: transparent; color: var(--ink); }
.btn.primary { background: var(--sig); border-color: var(--sig); color: #fff; }
.btn.primary:hover { background: var(--ink); border-color: var(--ink); color: var(--paper); }
.btn.sm { padding: 5px 11px; font-size: .82rem; }
.btn.ghost { border-color: transparent; color: var(--ink-2); text-decoration: underline; text-underline-offset: 3px; }
.btn.ghost:hover { background: transparent; color: var(--sig); }
.row { display: flex; flex-wrap: wrap; gap: 10px; align-items: center; margin-top: 16px; }
.pill { display: inline-block; font: 500 .7rem var(--mono); text-transform: uppercase; letter-spacing: .06em; padding: 1px 7px; border: 1px solid currentColor; color: var(--ink-2); white-space: nowrap; }
.pill-accent { color: var(--sig-ink); }
.pill-amber { color: var(--warn); }
.pill.t1 { color: var(--t1); } .pill.t2 { color: var(--t2); } .pill.t3 { color: var(--t3); }
.eyebrow { font: 500 .74rem var(--mono); text-transform: uppercase; letter-spacing: .1em; color: var(--ink-3); margin-bottom: .8em; }
.lede { color: var(--ink-2); font-size: 1.06rem; max-width: 60ch; }
.prog { height: 6px; background: var(--tint); }
.prog > div { height: 100%; background: var(--ink); transition: width .3s; }
.prog.big { height: 12px; }
.prog > div.lowp { background: var(--sig); }

/* ---------- home ---------- */
.cover { display: grid; grid-template-columns: 1fr 300px; border: 2px solid var(--rule-strong); background: var(--paper); margin-bottom: 44px; }
.cover-main { padding: 34px 36px 36px; border-right: 1px solid var(--rule-strong); }
.doc-id { font: .74rem var(--mono); color: var(--ink-3); letter-spacing: .06em; margin-bottom: 26px; display: flex; justify-content: space-between; border-bottom: 1px dashed var(--rule); padding-bottom: 10px; }
.hero-cta { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 24px; }
.spec { margin: 0; display: flex; flex-direction: column; }
.spec > div { padding: 16px 20px; border-bottom: 1px solid var(--rule); flex: 1; display: flex; flex-direction: column; justify-content: center; }
.spec > div:last-child { border-bottom: none; }
.spec dt { font: .7rem var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--ink-3); }
.spec dd { margin: 2px 0 0; font: 500 1.15rem var(--mono); }
.h-sec { display: flex; align-items: baseline; gap: 12px; font-size: 1.15rem; margin: 0 0 14px; padding-bottom: 8px; border-bottom: 1.5px solid var(--rule-strong); }
.h-sec span { font: 500 .78rem var(--mono); color: var(--sig); }
.cols { display: grid; grid-template-columns: 1fr 1fr; gap: 40px; margin-bottom: 44px; }
.home-block { margin-bottom: 44px; }
.toc { list-style: none; padding: 0; margin: 0; }
.toc li { margin: 0; border-bottom: 1px solid var(--rule); }
.toc a { display: grid; grid-template-columns: 34px 1fr auto; gap: 12px; align-items: baseline; padding: 14px 4px; color: var(--ink); text-decoration: none; }
.toc a:hover { background: var(--paper); }
.toc a:hover b { color: var(--sig); }
.toc-n { font: 500 1.4rem var(--serif); color: var(--ink-3); }
.toc-t b { display: block; font-size: 1.02rem; }
.toc-t small { color: var(--ink-3); font-size: .84rem; line-height: 1.4; display: block; margin-top: 2px; }
.toc-p { font: .78rem var(--mono); color: var(--ink-3); white-space: nowrap; }
.toc-extra { display: block; margin-top: 12px; font-size: .9rem; }
.papers { width: 100%; border-collapse: collapse; }
.papers td { padding: 14px 4px; border-bottom: 1px solid var(--rule); vertical-align: top; }
.papers td:last-child { text-align: right; white-space: nowrap; }
.papers b { font-size: 1.02rem; }
.papers small { display: block; color: var(--ink-3); font-size: .84rem; line-height: 1.4; margin-top: 2px; }
.papers .best-c { font: .78rem var(--mono); color: var(--ok); display: block; margin-top: 6px; }
.best { font: .76rem var(--mono); color: var(--ok); }
.plan { list-style: none; padding: 0; margin: 0; counter-reset: s; display: grid; grid-template-columns: repeat(5, 1fr); border: 1.5px solid var(--rule-strong); background: var(--paper); }
.plan li { counter-increment: s; margin: 0; padding: 16px 16px 18px; border-right: 1px solid var(--rule); font-size: .9rem; color: var(--ink-2); }
.plan li:last-child { border-right: none; }
.plan li::before { content: 'Step ' counter(s, decimal-leading-zero); display: block; font: .7rem var(--mono); color: var(--sig); letter-spacing: .06em; margin-bottom: 6px; text-transform: uppercase; }
.plan b { color: var(--ink); }
.extras { display: grid; grid-template-columns: 1fr 1fr; gap: 0; border-top: 1.5px solid var(--rule-strong); }
.link-card { display: block; padding: 18px 4px; color: var(--ink); text-decoration: none; border-bottom: 1px solid var(--rule); }
.extras .link-card:first-child { border-right: 1px solid var(--rule); padding-right: 24px; }
.extras .link-card:last-child { padding-left: 24px; }
.link-card p { color: var(--ink-3); font-size: .88rem; margin: 0; }
.link-card:hover h3 { color: var(--sig); }
.link-card h3::after { content: ' →'; color: var(--sig); }

/* generic card (tests page) */
.grid3 { display: grid; grid-template-columns: repeat(3, 1fr); border: 1.5px solid var(--rule-strong); background: var(--paper); }
.tcard { display: flex; flex-direction: column; padding: 22px; border-right: 1px solid var(--rule); color: var(--ink); text-decoration: none; }
.tcard:last-child { border-right: none; }
.tcard p { color: var(--ink-2); font-size: .9rem; flex: 1; }
.tcard-top { display: flex; justify-content: space-between; align-items: center; margin-bottom: 14px; }
.hist { display: flex; gap: 4px; margin: 4px 0 2px; }
.hist span { font: .76rem var(--mono); border: 1px solid var(--rule); padding: 1px 6px; }

/* ---------- page head ---------- */
.page-head { display: flex; justify-content: space-between; align-items: flex-end; gap: 20px; margin-bottom: 28px; padding-bottom: 18px; border-bottom: 2px solid var(--rule-strong); flex-wrap: wrap; }
.page-head h1 { margin-bottom: .2em; }
.page-head .lede { margin: 0; }
.back { display: inline-block; font: .8rem var(--mono); color: var(--ink-3); margin-bottom: 18px; text-decoration: none; }
.back:hover { color: var(--sig); }

/* ---------- learn ---------- */
.learn { display: grid; grid-template-columns: 230px 1fr; gap: 44px; align-items: start; }
.learn-nav { position: sticky; top: 84px; max-height: calc(100vh - 100px); overflow: auto; font-size: .88rem; padding-bottom: 20px; }
.ln-topics { display: grid; border-top: 1.5px solid var(--rule-strong); margin-bottom: 22px; }
.ln-topics a { display: flex; align-items: baseline; gap: 10px; padding: 9px 2px; color: var(--ink-2); font-weight: 500; text-decoration: none; border-bottom: 1px solid var(--rule); }
.ln-topics a span { font: 1.05rem var(--serif); color: var(--ink-3); width: 18px; }
.ln-topics a:hover { color: var(--ink); }
.ln-topics a.on { color: var(--ink); font-weight: 600; }
.ln-topics a.on span { color: var(--sig); }
.ln-h { font: .68rem var(--mono); text-transform: uppercase; letter-spacing: .1em; color: var(--ink-3); margin: 16px 0 6px; }
.ln-secs { display: grid; }
.ln-secs a { display: flex; align-items: center; gap: 9px; padding: 4px 0; color: var(--ink-2); text-decoration: none; }
.ln-secs a:hover { color: var(--ink); }
.ln-secs a.on { color: var(--sig-ink); font-weight: 600; }
.dot { width: 9px; height: 9px; border: 1.5px solid var(--ink-3); flex-shrink: 0; }
.dot.done { background: var(--ok); border-color: var(--ok); }
.ln-files { display: grid; gap: 4px; }
.src { font-size: .86rem; }
.src::after { content: ' ↗'; font-size: .85em; }
.learn-body { min-width: 0; }
.lb-head { margin-bottom: 26px; padding-bottom: 18px; border-bottom: 2px solid var(--rule-strong); }
.lb-head .lede { margin: 0; }
.note { background: var(--paper); border: 1px solid var(--rule); border-top: 2px solid var(--rule-strong); padding: 26px 32px 22px; margin-bottom: 26px; counter-increment: sec; }
.learn-body { counter-reset: sec; }
.note-h { display: flex; justify-content: space-between; align-items: baseline; gap: 12px; margin-bottom: 14px; }
.note-h h2 { margin: 0; }
.note-h h2::before { content: counter(sec) '.'; font: 500 .9rem var(--mono); color: var(--sig); margin-right: 10px; }
.readbox { display: flex; align-items: center; gap: 6px; font: .74rem var(--mono); text-transform: uppercase; letter-spacing: .05em; color: var(--ink-3); cursor: pointer; white-space: nowrap; user-select: none; }
.readbox:has(input:checked) { color: var(--ok); }
.readbox input { accent-color: var(--ok); margin: 0; }
.pager { display: flex; justify-content: space-between; gap: 12px; margin-top: 30px; flex-wrap: wrap; }

/* note components */
.two { display: grid; grid-template-columns: 1fr 1fr; gap: 0; margin: 12px 0 16px; border: 1px solid var(--rule); }
.two > * { padding: 14px 18px; }
.two > * + * { border-left: 1px solid var(--rule); }
.card-in h4 { margin-top: 0; }
.card-in ul { margin-bottom: 0; }
.card-in p:last-child { margin-bottom: 0; }
.example .two { border: none; margin: 0; }
.example .two > * { padding: 0 14px 0 0; }
.example .two > * + * { border-left: 1px dashed var(--rule); padding-left: 14px; }
.callout { padding: 10px 0 10px 16px; margin: 16px 0; font-size: .94rem; border-left: 3px solid; }
.callout > b:first-child { display: block; font: 600 .7rem var(--mono); text-transform: uppercase; letter-spacing: .1em; margin-bottom: 3px; }
.callout.tip { border-color: var(--ink); }
.callout.warn { border-color: var(--bad); background: linear-gradient(90deg, var(--bad-tint), transparent 70%); }
.callout.warn > b:first-child { color: var(--bad); }
.callout.key { border-color: var(--sig); background: linear-gradient(90deg, var(--sig-tint), transparent 70%); }
.callout.key > b:first-child { color: var(--sig-ink); }
.warn-inline { display: block; margin-top: 6px; font: .78rem var(--mono); color: var(--warn); }
.formula { font-family: var(--mono); font-size: .9rem; background: var(--bg); border: 1px solid var(--rule); border-left: 3px solid var(--ink); padding: 12px 16px; margin: 12px 0 16px; line-height: 1.95; overflow-x: auto; }
.example { border: 1px dashed var(--ink-3); padding: 14px 18px 4px; margin: 16px 0; position: relative; }
.ex-h { font: 600 .7rem var(--mono); text-transform: uppercase; letter-spacing: .1em; color: var(--ink-3); margin-bottom: 8px; }
.ex-h::before { content: 'Example — '; color: var(--sig); }
.chips { display: flex; flex-wrap: wrap; margin: 8px 0 14px; border: 1px solid var(--rule-strong); }
.chips span { flex: 1; text-align: center; font-weight: 500; font-size: .9rem; padding: 10px 12px; border-right: 1px solid var(--rule); }
.chips span:last-child { border-right: none; }
.steps { display: grid; margin: 12px 0 16px; border-top: 1px solid var(--rule); }
.steps > div { display: flex; gap: 14px; align-items: baseline; padding: 9px 2px; border-bottom: 1px solid var(--rule); }
.steps > div > b { flex-shrink: 0; min-width: 46px; color: var(--sig-ink); font: 600 .82rem var(--mono); }
.qc { margin: 14px 0; border: 1px solid var(--rule); }
.qc summary { cursor: pointer; padding: 10px 14px; font-weight: 500; list-style: none; display: flex; gap: 12px; align-items: baseline; }
.qc summary::-webkit-details-marker { display: none; }
.qc summary::after { content: '+ show'; margin-left: auto; font: .74rem var(--mono); color: var(--sig-ink); flex-shrink: 0; }
.qc[open] summary::after { content: '− hide'; }
.qc > div { padding: 0 14px 12px 14px; color: var(--ink-2); border-top: 1px dashed var(--rule); padding-top: 10px; }
.qc-tag { font: 600 .66rem var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--t3); flex-shrink: 0; }
.more { font-size: .9rem; color: var(--ink-3); }
.diagram { border: 1px solid var(--rule); padding: 20px; margin: 14px 0; display: grid; gap: 8px; justify-items: center; font-size: .86rem; background: var(--bg); }
.d-row { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; justify-content: center; }
.d-box { background: var(--paper); border: 1.5px solid var(--ink); padding: 9px 16px; font: 500 .84rem var(--mono); }
.d-box.sm { padding: 6px 10px; }
.d-bus { font: .76rem var(--mono); color: var(--ink-2); }
.d-down { font: 1.1rem var(--mono); line-height: 1; }
.d-cpu { border: 2px solid var(--sig); padding: 10px 14px; display: grid; gap: 6px; justify-items: center; }
.d-label { font: 600 .78rem var(--mono); color: var(--sig-ink); letter-spacing: .1em; }
.d-mini { font: .7rem var(--mono); color: var(--ink-3); }
.pow-table { display: grid; margin: 12px 0; border-top: 1px solid var(--rule); }
.pow-table > div { display: flex; gap: 14px; align-items: baseline; font: .88rem var(--mono); padding: 7px 2px; border-bottom: 1px solid var(--rule); flex-wrap: wrap; }
.pow-table b { min-width: 44px; color: var(--sig-ink); }
.pow-table span { word-spacing: .6em; }
.conv-map { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); margin: 10px 0 16px; border-top: 1px solid var(--rule); border-left: 1px solid var(--rule); }
.cm { padding: 12px 14px; display: flex; flex-direction: column; gap: 2px; border-right: 1px solid var(--rule); border-bottom: 1px solid var(--rule); }
.cm b { font-size: .95rem; }
.cm span { font-size: .86rem; color: var(--ink-2); }
.hex-grid { display: grid; grid-template-columns: repeat(8, 1fr); margin: 10px 0 16px; border-top: 1px solid var(--rule); border-left: 1px solid var(--rule); }
.hex-grid > div { padding: 8px 4px; text-align: center; display: flex; flex-direction: column; line-height: 1.3; border-right: 1px solid var(--rule); border-bottom: 1px solid var(--rule); }
.hex-grid b { font: 600 1.1rem var(--mono); color: var(--sig-ink); }
.hex-grid span { font: .8rem var(--mono); }
.hex-grid i { font: normal .68rem var(--mono); color: var(--ink-3); }
.weights { display: grid; grid-template-columns: repeat(8, 1fr); max-width: 460px; margin: 8px 0; border: 1px solid var(--ink); }
.weights span { text-align: center; font: 500 .82rem var(--mono); padding: 6px 0; border-right: 1px solid var(--rule); }
.weights span:last-child { border-right: none; }
.weights span:first-child { background: var(--sig); color: #fff; }
.ieee { display: grid; grid-template-columns: 1fr 8fr 23fr; margin: 10px 0 16px; border: 1.5px solid var(--ink); font: 500 .76rem var(--mono); text-align: center; }
.ieee span { padding: 10px 4px; }
.ieee .s { background: var(--sig); color: #fff; }
.ieee .e { border-left: 1.5px solid var(--ink); border-right: 1.5px solid var(--ink); background: var(--tint); }

/* tables */
.tbl-wrap { overflow-x: auto; margin: 12px 0 16px; }
.tbl { border-collapse: collapse; width: 100%; font-size: .9rem; }
.tbl th { text-align: left; font: 600 .7rem var(--mono); text-transform: uppercase; letter-spacing: .07em; color: var(--ink-2); padding: 7px 12px 7px 0; border-bottom: 1.5px solid var(--ink); white-space: nowrap; }
.tbl td { padding: 8px 12px 8px 0; border-bottom: 1px solid var(--rule); vertical-align: top; }
.tbl.mono td, .tbl.small td { font-family: var(--mono); font-size: .84rem; white-space: nowrap; }
.tbl.small td:first-child, .tbl.small td:nth-child(2) { font-family: var(--sans); white-space: normal; }
.tbl.mono.small td { font-family: var(--mono); }
.tool-out .tbl, .sol .tbl, .work .tbl { display: block; overflow-x: auto; }
p.tip { border-left: 3px solid var(--warn); padding: 4px 12px; font-size: .9rem; }

/* ---------- cheat sheet ---------- */
.cheat { display: grid; grid-template-columns: repeat(3, 1fr); border: 2px solid var(--rule-strong); background: var(--paper); }
.cheat section { padding: 20px 22px; border-right: 1px solid var(--rule); }
.cheat section:last-child { border-right: none; }
.cheat h3 { font: 600 .78rem var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--sig-ink); padding-bottom: 8px; border-bottom: 1px solid var(--ink); }
.cheat ul { list-style: none; padding: 0; font-size: .88rem; }
.cheat li { margin: 0; padding: 6px 0; border-bottom: 1px dotted var(--rule); }

/* ---------- test intro ---------- */
.intro, .results { max-width: 840px; margin: 0 auto; }
.intro-stats { display: flex; flex-wrap: wrap; margin: 24px 0; border: 1.5px solid var(--rule-strong); background: var(--paper); }
.intro-stats > div { padding: 12px 20px; display: flex; flex-direction: column; border-right: 1px solid var(--rule); flex: 1; min-width: 90px; }
.intro-stats > div:last-child { border-right: none; }
.intro-stats b { font: 500 1.4rem var(--mono); }
.intro-stats span { font: .7rem var(--mono); color: var(--ink-3); text-transform: uppercase; letter-spacing: .06em; }
.modes { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin: 10px 0 18px; }
.mode { text-align: left; background: var(--paper); border: 1.5px solid var(--ink); padding: 20px 22px; cursor: pointer; color: var(--ink); font: inherit; display: flex; flex-direction: column; gap: 6px; transition: box-shadow .12s, transform .12s; }
.mode:hover { box-shadow: 5px 5px 0 var(--sig); transform: translate(-2px, -2px); }
.mode b { font-size: 1.08rem; }
.mode b::after { content: ' →'; color: var(--sig); }
.mode span { color: var(--ink-2); font-size: .9rem; }
.hint { color: var(--ink-3); font-size: .84rem; }

/* ---------- runner ---------- */
.runner { max-width: 1100px; margin: -14px auto 0; }
.run-bar { display: flex; align-items: center; gap: 18px; background: var(--paper); border: 1.5px solid var(--rule-strong); padding: 8px 12px; position: sticky; top: 66px; z-index: 20; }
.run-bar .back { margin: 0; font-size: 1rem; padding: 2px 8px; color: var(--ink-2); }
.run-title { display: flex; flex-direction: column; line-height: 1.2; }
.run-title span { font: .68rem var(--mono); color: var(--ink-3); text-transform: uppercase; letter-spacing: .06em; }
.run-prog { flex: 1; display: flex; align-items: center; gap: 10px; font: .8rem var(--mono); color: var(--ink-3); }
.run-prog .prog { flex: 1; }
.timer { font: 500 1rem var(--mono); padding: 3px 10px; border: 1px solid var(--rule); }
.timer.low { border-color: var(--bad); color: var(--bad); }
.run-main { display: grid; grid-template-columns: 1fr 250px; gap: 22px; margin-top: 20px; align-items: start; }
.qcard { background: var(--paper); border: 1px solid var(--rule); border-top: 2px solid var(--rule-strong); padding: 26px 30px 28px; }
.q-meta { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; margin-bottom: 18px; }
.qn { font: 600 .9rem var(--mono); }
.qn small { color: var(--ink-3); font-weight: 400; }
.flag { margin-left: auto; border: 1px solid var(--rule); background: transparent; color: var(--ink-3); padding: 3px 9px; font: .74rem var(--mono); cursor: pointer; text-transform: uppercase; letter-spacing: .05em; }
.flag:hover { border-color: var(--ink); color: var(--ink); }
.flag.on { border-color: var(--warn); color: var(--warn); background: var(--warn-tint); }
/* calculator button (js/calc.js) */
.q-meta .calc-btn { margin-left: 8px; }
.q-meta.calc-row { justify-content: flex-end; margin-bottom: 6px; }
.q-text { font: 400 1.22rem/1.5 var(--serif); margin-bottom: 22px; }
.q-text.big { font-size: 1.32rem; }
.opts { display: grid; border-top: 1px solid var(--rule); }
.opt { display: flex; align-items: center; gap: 16px; width: 100%; text-align: left; padding: 13px 10px; border: none; border-bottom: 1px solid var(--rule); background: transparent; color: var(--ink); font: 400 1rem var(--sans); cursor: pointer; transition: background .1s; }
.opt:hover:not(:disabled) { background: var(--bg); }
.opt:hover:not(:disabled) .L { border-color: var(--ink); }
.opt .L { width: 28px; height: 28px; border: 1.5px solid var(--ink-3); display: grid; place-items: center; font: 600 .82rem var(--mono); flex-shrink: 0; }
.opt .T { flex: 1; }
.opt em { font: .7rem var(--mono); color: var(--ink-3); font-style: normal; text-transform: uppercase; }
.opt.sel { background: var(--bg); }
.opt.sel .L { background: var(--ink); border-color: var(--ink); color: var(--paper); }
.opt.right { background: var(--ok-tint); }
.opt.right .L { background: var(--ok); border-color: var(--ok); color: #fff; }
.opt.wrong { background: var(--bad-tint); }
.opt.wrong .L { background: var(--bad); border-color: var(--bad); color: #fff; }
.opt.dim { color: var(--ink-3); }
.opt:disabled { cursor: default; }
.opts.small .opt { padding: 7px 8px; font-size: .9rem; cursor: default; }
.opts.small .opt .L { width: 22px; height: 22px; font-size: .72rem; }
.explain { margin-top: 18px; padding: 12px 16px; border-left: 3px solid var(--ink); background: var(--bg); font-size: .94rem; }
.explain > b:first-child { display: block; margin-bottom: 4px; font: 600 .74rem var(--mono); text-transform: uppercase; letter-spacing: .08em; }
.explain.good { border-color: var(--ok); }
.explain.good > b:first-child { color: var(--ok); }
.explain.bad { border-color: var(--bad); }
.explain.bad > b:first-child { color: var(--bad); }
/* why each option (js/why.js) */
.why { margin-top: 12px; padding-top: 10px; border-top: 1px dashed var(--rule); }
.why > b { display: block; margin-bottom: 6px; font: 600 .74rem var(--mono); text-transform: uppercase; letter-spacing: .08em; }
.why ul { list-style: none; margin: 0; padding: 0; display: grid; gap: 6px; }
.why li { display: flex; gap: 10px; align-items: baseline; line-height: 1.45; }
.why li .L { flex: 0 0 auto; font: 600 .78rem var(--mono); min-width: 2.6em; }
.why li.ok .L { color: var(--ok); }
.why li.no .L { color: var(--bad); }
.why li.ok .L::after { content: " ✓"; }
.why li.no .L::after { content: " ✗"; }
.why li.mine .W { font-weight: 500; }
.why li em { font-style: normal; font: 600 .7rem var(--mono); text-transform: uppercase; letter-spacing: .06em; opacity: .7; margin-left: 4px; }
.q-foot { display: flex; justify-content: space-between; margin-top: 16px; }
.qnav { background: var(--paper); border: 1px solid var(--rule); padding: 14px; position: sticky; top: 132px; }
.qnav-h { font: 600 .74rem var(--mono); text-transform: uppercase; letter-spacing: .08em; margin-bottom: 10px; display: flex; flex-direction: column; gap: 4px; }
.legend { display: flex; gap: 10px; font: 400 .68rem var(--mono); color: var(--ink-3); align-items: center; text-transform: none; letter-spacing: 0; }
.legend i { width: 9px; height: 9px; display: inline-block; margin-right: -6px; }
.legend i.a { background: var(--ink); }
.legend i.f { background: var(--warn); }
.qgrid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 3px; margin-bottom: 12px; }
.qgrid button { aspect-ratio: 1; border: 1px solid var(--rule); background: transparent; color: var(--ink-2); font: .74rem var(--mono); cursor: pointer; position: relative; padding: 0; }
.qgrid button:hover { border-color: var(--ink); }
.qgrid button.a { background: var(--ink); color: var(--paper); border-color: var(--ink); }
.qgrid button.ok { background: var(--ok); color: #fff; border-color: var(--ok); }
.qgrid button.bad { background: var(--bad); color: #fff; border-color: var(--bad); }
.qgrid button.f::after { content: ''; position: absolute; top: 0; right: 0; border: 5px solid var(--warn); border-left-color: transparent; border-bottom-color: transparent; }
.qgrid button.cur { outline: 2px solid var(--sig); outline-offset: 1px; }
.live { font: .78rem var(--mono); color: var(--ink-2); margin-bottom: 10px; padding: 8px 0; border-top: 1px solid var(--rule); border-bottom: 1px solid var(--rule); }
.live b { color: var(--ok); font-size: 1rem; }

/* ---------- results ---------- */
.res-head { display: grid; grid-template-columns: auto 1fr; gap: 0; border: 2px solid var(--rule-strong); background: var(--paper); margin-bottom: 0; }
.score-big { padding: 24px 30px; border-right: 1px solid var(--rule-strong); display: flex; align-items: baseline; justify-content: center; }
.score-big b { font: 500 4.4rem/1 var(--serif); letter-spacing: -.03em; }
.score-big span { font: 1.1rem var(--mono); color: var(--ink-3); margin-left: 4px; }
.res-info { padding: 22px 26px; }
.res-info h1 { font-size: 2rem; margin-bottom: .1em; }
.res-info .lede { margin: 0; font-size: 1rem; }
.strip { display: grid; grid-template-columns: repeat(50, 1fr); gap: 2px; padding: 10px; border: 2px solid var(--rule-strong); border-top: none; background: var(--paper); margin-bottom: 26px; }
.strip i { height: 18px; background: var(--rule); }
.strip i.ok { background: var(--ok); }
.strip i.bad { background: var(--bad); }
.bars { border-top: 1.5px solid var(--rule-strong); display: grid; margin-bottom: 32px; }
.bar { display: grid; grid-template-columns: 200px 1fr 54px; gap: 16px; align-items: center; font-size: .9rem; padding: 10px 0; border-bottom: 1px solid var(--rule); }
.bar-r { font: .86rem var(--mono); text-align: right; }
.review-h { display: flex; justify-content: space-between; align-items: center; gap: 12px; flex-wrap: wrap; margin-bottom: 14px; padding-bottom: 10px; border-bottom: 2px solid var(--rule-strong); }
.review-h h2 { margin: 0; }
.seg { display: inline-flex; border: 1.5px solid var(--ink); }
.seg button, .seg a { border: none; border-right: 1px solid var(--ink); background: transparent; padding: 6px 13px; font: 500 .8rem var(--mono); color: var(--ink-2); cursor: pointer; text-decoration: none; }
.seg > :last-child { border-right: none; }
.seg .on { background: var(--ink); color: var(--paper); }
.seg.wide { display: flex; flex-wrap: wrap; margin-bottom: 26px; border: none; border-top: 1.5px solid var(--ink); }
.seg.wide a { display: flex; flex-direction: column; line-height: 1.3; padding: 10px 18px 10px 0; margin-right: 18px; border: none; border-top: 3px solid transparent; margin-top: -2px; font-family: var(--sans); font-weight: 600; font-size: .9rem; }
.seg.wide a.on { background: transparent; color: var(--ink); border-top-color: var(--sig); }
.seg.wide small { font: 400 .74rem var(--sans); color: var(--ink-3); }
.rq { background: var(--paper); border: 1px solid var(--rule); border-left: 3px solid var(--ok); padding: 18px 22px; margin-bottom: 14px; }
.rq.bad { border-left-color: var(--bad); }
.rq .q-text { font-size: 1.05rem; margin-bottom: 12px; }
.mark { margin-left: auto; font: 600 .74rem var(--mono); text-transform: uppercase; letter-spacing: .06em; }
.rq.ok .mark { color: var(--ok); }
.rq.bad .mark { color: var(--bad); }
.empty { text-align: center; color: var(--ink-3); padding: 30px; font-family: var(--mono); }

/* ---------- practice ---------- */
.score { display: flex; border: 1.5px solid var(--ink); background: var(--paper); }
.score > div { padding: 6px 16px; text-align: center; min-width: 78px; border-right: 1px solid var(--rule); }
.score > div:last-child { border-right: none; }
.score b { display: block; font: 500 1.3rem var(--mono); }
.score span { font: .66rem var(--mono); color: var(--ink-3); text-transform: uppercase; letter-spacing: .06em; }
.drill-tabs { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 20px; }
.drill-tabs button { border: 1px solid var(--rule); background: var(--paper); color: var(--ink-2); padding: 6px 12px; font: 500 .85rem var(--sans); cursor: pointer; display: flex; gap: 8px; align-items: baseline; }
.drill-tabs button small { font: .66rem var(--mono); color: var(--ink-3); }
.drill-tabs button:hover { border-color: var(--ink); color: var(--ink); }
.drill-tabs button.on { background: var(--ink); border-color: var(--ink); color: var(--paper); }
.drill-tabs button.on small { color: var(--sig); }
.drill { max-width: 840px; }
.answer { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; }
.answer input:not([type]) { flex: 1; min-width: 200px; padding: 11px 14px; border: none; border-bottom: 2px solid var(--ink); background: var(--bg); color: var(--ink); font-size: 1.1rem; }
.answer input:focus { outline: none; border-bottom-color: var(--sig); }
.ovf { display: flex; align-items: center; gap: 6px; font: .82rem var(--mono); padding: 0 6px; cursor: pointer; }
.work { margin-top: 12px; padding-top: 12px; border-top: 1px dashed var(--rule); font-weight: 400; }

/* ---------- tutorials ---------- */
.tut-head { display: flex; justify-content: space-between; align-items: baseline; flex-wrap: wrap; gap: 10px; margin-bottom: 12px; }
.tut-head h2 { margin: 0; }
.tut-head .row { margin: 0; }
.tut-list { display: grid; border-top: 1.5px solid var(--rule-strong); }
.ans { border-bottom: 1px solid var(--rule); }
.ans summary { list-style: none; cursor: pointer; padding: 12px 4px; display: flex; justify-content: space-between; gap: 16px; align-items: baseline; }
.ans summary::-webkit-details-marker { display: none; }
.ans summary:hover { background: var(--paper); }
.ans summary:hover .aq { color: var(--sig-ink); }
.aq { font-weight: 500; }
.aa { font: .8rem var(--mono); color: var(--ink-3); text-align: right; flex-shrink: 0; max-width: 45%; overflow: hidden; text-overflow: ellipsis; }
.ans[open] .aa { color: var(--ok); }
.ans[open] { background: var(--paper); }
.sol { padding: 6px 20px 18px; border-top: 1px dashed var(--rule); }

/* ---------- tools ---------- */
.tool-nav { display: flex; flex-wrap: wrap; gap: 4px 16px; margin-bottom: 22px; font-size: .88rem; }
.tools { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 22px; }
.tool { background: var(--paper); border: 1px solid var(--rule); border-top: 2px solid var(--rule-strong); padding: 18px 22px 22px; min-width: 0; }
.tool-h { display: flex; justify-content: space-between; align-items: baseline; gap: 8px; }
.tool-h h3 { margin: 0; }
.tool-form { display: flex; flex-wrap: wrap; gap: 12px; margin: 16px 0; }
.tool-form label { display: flex; flex-direction: column; gap: 4px; font: .68rem var(--mono); color: var(--ink-3); text-transform: uppercase; letter-spacing: .06em; flex: 1; min-width: 100px; }
.tool-form label.wide { flex-basis: 100%; }
.tool-form input, .tool-form select { padding: 8px 10px; border: none; border-bottom: 1.5px solid var(--ink); background: var(--bg); color: var(--ink); font: 400 .95rem var(--sans); text-transform: none; letter-spacing: 0; border-radius: 0; }
.tool-form input.mono { font-family: var(--mono); }
.tool-form input:focus, .tool-form select:focus { outline: none; border-bottom-color: var(--sig); }
.tool-out { font-size: .92rem; border-left: 3px solid var(--ink); padding: 4px 0 4px 16px; overflow-x: auto; }
.tool-out p:last-child { margin-bottom: 0; }

/* ---------- responsive ---------- */
@media (max-width: 960px) {
  .cover { grid-template-columns: 1fr; }
  .cover-main { border-right: none; border-bottom: 1px solid var(--rule-strong); }
  .spec { flex-direction: row; flex-wrap: wrap; }
  .spec > div { flex: 1 1 50%; border-right: 1px solid var(--rule); }
  .cols { grid-template-columns: 1fr; gap: 36px; }
  .plan { grid-template-columns: 1fr; }
  .plan li { border-right: none; border-bottom: 1px solid var(--rule); }
  .plan li:last-child { border-bottom: none; }
  .grid3, .cheat { grid-template-columns: 1fr; }
  .tcard, .cheat section { border-right: none; border-bottom: 1px solid var(--rule); }
  .learn { grid-template-columns: 1fr; gap: 0; }
  .learn-nav { position: static; max-height: none; margin-bottom: 18px; }
  .ln-topics { grid-template-columns: repeat(3, 1fr); border-top: none; border-bottom: 1.5px solid var(--rule-strong); }
  .ln-topics a { border-bottom: none; }
  .ln-h, .ln-secs, .ln-files { display: none; }
  .run-main { grid-template-columns: 1fr; }
  .qnav { position: static; }
  .qgrid { grid-template-columns: repeat(10, 1fr); }
  .tools { grid-template-columns: 1fr; }
}
@media (max-width: 680px) {
  body { font-size: 15px; padding-bottom: 64px; }
  .wrap { padding: 0 16px; }
  #app { padding-top: 22px; }
  .top-in { padding: 0 16px; height: 52px; justify-content: space-between; }
  .logo-txt small { display: none; }
  .courses-btn { margin-left: auto; margin-right: -4px; }
  .courses-btn .wd { display: none; }
  .top-in { gap: 10px; }
  .logo { min-width: 0; flex-shrink: 1; }
  .logo-txt { min-width: 0; }
  .logo-txt b { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
  .nav { position: fixed; bottom: 0; left: 0; right: 0; height: auto; background: var(--paper); border-top: 2px solid var(--rule-strong); padding: 0 0 env(safe-area-inset-bottom); z-index: 60; }
  .nav a { flex: 1; flex-direction: column; gap: 0; font-size: .7rem; padding: 7px 2px 8px; border-bottom: none; border-top: 3px solid transparent; margin: -2px 0 0; justify-content: center; }
  .nav a.on { border-top-color: var(--sig); }
  .nav .hide-sm { display: none; }
  .cover-main { padding: 22px 20px 24px; }
  .doc-id { margin-bottom: 18px; flex-direction: column; gap: 2px; }
  .spec > div { padding: 10px 16px; }
  .spec dd { font-size: 1rem; }
  .extras { grid-template-columns: 1fr; }
  .extras .link-card:first-child { border-right: none; padding-right: 4px; }
  .extras .link-card:last-child { padding-left: 4px; }
  .two { grid-template-columns: 1fr; }
  .two > * + * { border-left: none; border-top: 1px solid var(--rule); }
  .example .two > * + * { border-top: 1px dashed var(--rule); padding: 10px 0 0; border-left: none; }
  .modes { grid-template-columns: 1fr; }
  .note { padding: 20px 16px 16px; }
  .note-h { flex-direction: column; gap: 6px; }
  .ln-topics { grid-template-columns: 1fr; }
  .chips span { flex-basis: 50%; border-bottom: 1px solid var(--rule); }
  .hex-grid { grid-template-columns: repeat(4, 1fr); }
  .qcard { padding: 18px 16px 20px; }
  .q-text { font-size: 1.1rem; }
  .run-bar { flex-wrap: wrap; gap: 10px; top: 58px; }
  .run-prog { order: 5; flex-basis: 100%; }
  .run-title { flex: 1; }
  .qgrid { gap: 2px; }
  .qgrid button { font-size: .62rem; }
  .res-head { grid-template-columns: 1fr; }
  .score-big { border-right: none; border-bottom: 1px solid var(--rule-strong); padding: 18px; }
  .strip { gap: 1px; padding: 8px; }
  .strip i { height: 14px; }
  .bar { grid-template-columns: 1fr 50px; }
  .bar .prog { grid-column: 1 / -1; grid-row: 2; }
  .ans summary { flex-direction: column; gap: 2px; }
  .aa { max-width: 100%; text-align: left; }
  .page-head { margin-bottom: 20px; }
  .score > div { min-width: 64px; padding: 6px 10px; }
}

/* ---------- print (cheat sheet) ---------- */
@media print {
  .top, .foot, .page-head .btn { display: none !important; }
  body { background: #fff; color: #000; }
  .cheat { grid-template-columns: 1fr 1fr 1fr; }
  .cheat section { padding: 10px; font-size: 11px; }
}