/* AI Tech Institute colourways: paper, ink, oxide. Fraunces for display, Inter Tight for text, JetBrains Mono for labels. */
:root {
  --paper: #f2ede3; --paper-deep: #ece5d6; --stone: #ddd4c0; --fog: #b8ae96;
  --ink: #1b1814; --ink-soft: #4a4239; --ink-mute: #7a6f5f;
  --oxide: #8b2d1f; --oxide-deep: #5c1e14; --oxide-tint: rgba(139, 45, 31, .08); --oxide-tint-2: rgba(139, 45, 31, .14);
  --rule: rgba(27, 24, 20, .14); --rule-strong: rgba(27, 24, 20, .30);
  --serif: "Fraunces", Georgia, serif; --sans: "Inter Tight", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; --mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, monospace;
}
* { box-sizing: border-box; }
html, body { margin: 0; height: 100%; font: 16px/1.6 var(--sans); color: var(--ink-soft); background: var(--paper); -webkit-font-smoothing: antialiased; }
body { display: grid; grid-template-columns: 360px 1fr; height: 100vh; }
a { color: var(--oxide); text-decoration: none; } a:hover { text-decoration: underline; text-underline-offset: 3px; }
button { font: inherit; color: var(--ink); background: none; border: 1px solid var(--rule-strong); border-radius: 999px; padding: 5px 14px; cursor: pointer; }
button:hover { background: var(--ink); color: var(--paper); border-color: var(--ink); }
button:disabled { opacity: .35; cursor: default; } button:disabled:hover { background: none; color: var(--ink); border-color: var(--rule-strong); }
.eyebrow { font: 500 .68rem/1 var(--mono); letter-spacing: .14em; text-transform: uppercase; color: var(--ink-mute); }
.eyebrow::before { content: "●"; color: var(--oxide); font-size: .55rem; margin-right: .6em; vertical-align: middle; }

#side { background: var(--paper-deep); border-right: 1px solid var(--rule); display: flex; flex-direction: column; min-height: 0; }
.side-head { padding: 20px 22px 16px; border-bottom: 1px solid var(--rule); }
.brand { display: flex; align-items: center; gap: 10px; margin-bottom: 18px; color: var(--ink); font: 500 .82rem var(--serif); }
.brand .mark { width: 22px; height: 22px; background: var(--oxide); color: var(--paper); border-radius: 3px; display: grid; place-items: center; font: 500 15px/1 var(--serif); }
.brand a { color: var(--ink); }
.course-title { font: 300 1.9rem/1.05 var(--serif); color: var(--ink); letter-spacing: -.02em; margin: 6px 0 4px; }
.course-title .dot { color: var(--oxide); }
.learner { font: 400 .72rem var(--mono); color: var(--ink-mute); letter-spacing: .04em; margin-bottom: 14px; }
.overall-bar { height: 3px; background: var(--rule); border-radius: 2px; overflow: hidden; }
#overall-fill { height: 100%; width: 0; background: var(--oxide); transition: width .4s; }
.overall-text { font: 400 .7rem var(--mono); color: var(--ink-mute); margin-top: 6px; letter-spacing: .02em; }
.continue { margin-top: 14px; width: 100%; text-align: left; background: var(--ink); color: var(--paper); border-color: var(--ink); padding: 11px 16px; border-radius: 12px; line-height: 1.3; font-weight: 500; }
.continue:hover { background: var(--oxide); border-color: var(--oxide); color: var(--paper); }
.continue small { display: block; opacity: .7; font: 400 .7rem var(--mono); margin-top: 4px; letter-spacing: .02em; }
.continue .arrow { float: right; }
.tree { overflow-y: auto; flex: 1; padding: 6px 0 16px; }
.tier { padding: 18px 22px 6px; }
.stage-row { display: grid; grid-template-columns: 30px 1fr auto; gap: 12px; align-items: center; padding: 10px 22px 10px 16px; cursor: pointer; user-select: none; border-left: 3px solid transparent; }
.stage-row:hover { background: var(--oxide-tint); }
.stage.open > .stage-row { background: rgba(27,24,20,.04); }
.stage.current > .stage-row { background: var(--oxide-tint); border-left-color: var(--oxide); }
.stage-name { font: 500 .92rem/1.25 var(--sans); color: var(--ink); }
.stage-sub { font: 400 .68rem var(--mono); color: var(--ink-mute); margin-top: 3px; letter-spacing: .02em; }
.ring { width: 30px; height: 30px; }
.ring circle { fill: none; stroke-width: 2.6; }
.ring .track { stroke: var(--rule); }
.ring .fill { stroke: var(--oxide); stroke-linecap: round; transform: rotate(-90deg); transform-origin: 50% 50%; transition: stroke-dasharray .4s; }
.ring text { font: 500 8.5px var(--mono); fill: var(--ink-mute); text-anchor: middle; dominant-baseline: central; }
.stage-hours { font: 500 .58rem var(--mono); color: var(--oxide); letter-spacing: .12em; text-transform: uppercase; }
.chev { display: inline-block; transition: transform .15s; color: var(--fog); font-size: 9px; margin-left: 6px; vertical-align: middle; }
.stage.open .chev { transform: rotate(90deg); }
.rungs { display: none; padding: 2px 0 10px; }
.stage.open .rungs { display: block; }
.part { padding: 10px 22px 3px 58px; font: 500 .62rem var(--mono); color: var(--ink-mute); letter-spacing: .12em; text-transform: uppercase; }
.rung { display: grid; grid-template-columns: 16px 1fr auto; gap: 10px; align-items: baseline; padding: 6px 22px 6px 58px; font-size: .88rem; cursor: pointer; border-left: 3px solid transparent; color: var(--ink-soft); }
.rung:hover { background: var(--oxide-tint); }
.rung.active { background: var(--oxide-tint-2); border-left-color: var(--oxide); color: var(--ink); }
.rung.done .rung-title { color: var(--ink-mute); }
.rung .mark { font-size: .8rem; color: var(--fog); text-align: center; }
.rung.done .mark { color: var(--oxide); }
.rung .mins { font: 400 .66rem var(--mono); color: var(--ink-mute); }
.side-foot { padding: 12px 22px 16px; border-top: 1px solid var(--rule); font: 400 .72rem var(--mono); color: var(--ink-mute); letter-spacing: .02em; }
.side-foot a { color: var(--ink-soft); } .side-foot a:hover { color: var(--oxide); }
.updated { margin-top: 6px; font-size: .66rem; }
.by { margin-top: 8px; font: italic 300 .78rem var(--serif); color: var(--ink-mute); }

#backdrop { position: fixed; inset: 0; background: rgba(27, 24, 20, .35); z-index: 20; }
#backdrop[hidden] { display: none; }
.menu { display: none; }

#main { min-height: 0; overflow-y: auto; }
.topbar { position: sticky; top: 0; background: var(--paper); border-bottom: 1px solid var(--rule); display: flex; align-items: center; gap: 12px; padding: 12px 28px; z-index: 2; }
.crumbs { font: 400 .72rem var(--mono); color: var(--ink-mute); letter-spacing: .03em; text-transform: uppercase; min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.crumbs b { color: var(--ink); font-weight: 500; }
.pill { display: inline-block; font: 500 .6rem var(--mono); letter-spacing: .1em; text-transform: uppercase; padding: 3px 9px; border-radius: 999px; border: 1px solid var(--rule-strong); color: var(--ink-mute); margin-left: 8px; vertical-align: middle; }
.pill.done { border-color: var(--oxide); color: var(--oxide); }
.pill.current { background: var(--oxide); border-color: var(--oxide); color: var(--paper); }
.kernel { margin-left: auto; font: 400 .66rem var(--mono); letter-spacing: .08em; text-transform: uppercase; color: var(--ink-mute); white-space: nowrap; }
.kernel::before { content: ""; display: inline-block; width: 7px; height: 7px; border-radius: 50%; background: var(--fog); margin-right: 6px; vertical-align: middle; }
.kernel.ready { color: var(--oxide); }
.kernel.ready::before { background: var(--oxide); }
.kernel.busy { color: var(--ink); }
.kernel.busy::before { background: var(--ink); }
.pager { display: flex; gap: 8px; }
.pager button { font: 500 .78rem var(--mono); letter-spacing: .02em; min-height: 40px; padding: 8px 16px; }
.content { max-width: 760px; padding: 28px 32px 96px; }
.rung-head { margin: 8px 0 8px; }
.rung-head h1 { margin-top: 4px; }
.content h1 { font: 300 2.7rem/1.05 var(--serif); color: var(--ink); letter-spacing: -.03em; margin: 8px 0 8px; }
.content h1::after { content: "."; color: var(--oxide); }
.content .lede { font: italic 300 1.15rem/1.45 var(--serif); color: var(--ink-mute); margin-top: 0; }
.content h2 { font: 400 1.45rem/1.2 var(--serif); color: var(--ink); letter-spacing: -.015em; margin-top: 36px; padding-top: 18px; border-top: 1px solid var(--rule); }
.content h3 { font: 500 1.05rem/1.3 var(--sans); color: var(--ink); margin-top: 28px; }
.content p, .content li { font-size: 1.05rem; line-height: 1.65; }
.content strong { color: var(--ink); font-weight: 600; }
.content pre { background: var(--paper-deep); border: 1px solid var(--rule); padding: 14px 16px; border-radius: 6px; overflow-x: auto; font: 400 .82rem/1.55 var(--mono); color: var(--ink); margin: 0; }
.content code { font-family: var(--mono); font-size: .85em; background: var(--paper-deep); padding: 1px 5px; border-radius: 3px; color: var(--ink); }
.content pre code { background: none; padding: 0; font-size: inherit; }
.content blockquote { margin: 14px 0; padding: 4px 18px; border-left: 2px solid var(--oxide); color: var(--ink-mute); font: italic 300 1.05rem/1.5 var(--serif); }
.content hr { border: none; border-top: 1px solid var(--rule); }
.content li { margin: 4px 0; }
.content a { text-decoration: underline; text-decoration-color: var(--stone); text-underline-offset: 3px; }
.content a:hover { text-decoration-color: var(--oxide); }
.check-card { margin: 10px 0 20px; padding: 12px 16px; border: 1px solid var(--rule); border-radius: 6px; background: var(--paper-deep); }
.check-card .row { display: flex; gap: 8px; align-items: center; flex-wrap: wrap; }
.check-card button { font: 500 .72rem var(--mono); letter-spacing: .08em; text-transform: uppercase; }
.check-card button.on { background: var(--oxide); color: var(--paper); border-color: var(--oxide); }
.check-card .hint { color: var(--ink-mute); font-size: .8rem; margin-top: 8px; }
.ideas { margin: 18px 0 8px; border: 1px solid var(--rule); border-radius: 12px; background: var(--paper-deep); padding: 4px 16px 8px; }
.ideas summary { cursor: pointer; font: 500 .95rem var(--sans); color: var(--ink); padding: 10px 0; }
.ideas p, .ideas li { font-size: .98rem; }
.run-rung { margin: 18px 0 0; }
.py-cell { margin: 8px 0 22px; border: 1px solid var(--rule); border-radius: 12px; overflow: hidden; background: var(--paper); }
.py-lines { padding: 6px 0; background: var(--paper-deep); }
.py-line { display: grid; grid-template-columns: max-content minmax(150px, 220px); gap: 8px 22px; align-items: baseline; padding: 7px 16px; }
.py-line + .py-line { border-top: 1px solid rgba(27, 24, 20, .06); }
.py-line.blank { min-height: 10px; padding: 0; border-top: none; }
.src { font: 400 .84rem/1.45 var(--mono); color: var(--ink); white-space: pre; overflow-x: auto; min-width: 0; }
.gloss { font: italic 400 .98rem/1.35 var(--serif); color: var(--ink-mute); }
.cell-bar { padding: 14px 16px 8px; background: var(--paper); }
.cell-kicker { font: 500 .62rem var(--mono); letter-spacing: .12em; text-transform: uppercase; color: var(--ink-mute); }
.cell-title { font: 500 1.05rem/1.3 var(--sans); color: var(--ink); margin-top: 2px; }
.cell-foot { display: flex; justify-content: flex-end; padding: 8px 12px 12px; background: var(--paper-deep); }
.cell-foot button.run { background: var(--ink); color: var(--paper); border-color: var(--ink); font: 500 .9rem var(--sans); min-height: 44px; min-width: 96px; padding: 8px 22px; }
.cell-foot button.run:hover { background: var(--oxide); border-color: var(--oxide); }
.cell-out { display: none; margin: 0; padding: 12px 16px 14px; background: var(--ink); color: var(--paper); font: 400 .8rem/1.55 var(--mono); white-space: pre; overflow-x: auto; }
.cell-out.visible { display: block; }
.cell-out.err { color: #f0c2b8; }
.cell-out img { display: block; max-width: 100%; height: auto; margin-top: 12px; background: var(--paper); border-radius: 4px; }
.err { padding: 30px; color: var(--oxide-deep); background: var(--oxide-tint); margin: 24px; border-radius: 6px; }
@media (max-width: 860px) {
  body { grid-template-columns: 1fr; }
  .menu { display: inline-flex; align-items: center; min-height: 40px; }
  #side { position: fixed; top: 0; bottom: 0; left: 0; width: min(88vw, 380px); z-index: 30; transform: translateX(-105%); transition: transform .2s ease; }
  body.nav-open #side { transform: none; }
  .topbar { padding: 10px 14px; gap: 8px; }
  .pager { position: fixed; left: 0; right: 0; bottom: 0; z-index: 4; display: grid; grid-template-columns: 1fr 1fr; gap: 8px; padding: 10px 14px calc(10px + env(safe-area-inset-bottom)); background: var(--paper); border-top: 1px solid var(--rule); }
  .pager button { width: 100%; }
  .content { padding: 18px 18px calc(92px + env(safe-area-inset-bottom)); }
  .content h1 { font-size: 2.15rem; }
  .py-line { grid-template-columns: 1fr; gap: 3px; padding: 10px 14px 12px; }
  .gloss { color: var(--ink-soft); border-left: 2px solid var(--oxide); padding-left: 8px; }
  .cell-foot button.run { width: 100%; }
  .rung { min-height: 44px; align-items: center; }
}