:root {
  --bg: #F5F6F8; --surface: #FFFFFF; --ink: #11141B; --muted: #4B5363;
  --line: #DDE1E8; --line-soft: #EDEFF3; --line-strong: #C9CFD9;
  --on-dark: #C4CAD6;
  --radius-card: 14px; --radius-control: 10px; --radius-chip: 999px;
  --display: "Bricolage Grotesque", system-ui, sans-serif;
  --body: "Instrument Sans", system-ui, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, monospace;
  --gutter: clamp(16px, 4vw, 40px);
  --c: var(--ink); --tint: var(--line-soft); --chip: var(--ink);
}
.t-fundamentals { --c: oklch(0.48 0.17 255); --tint: oklch(0.95 0.03 255); --chip: oklch(0.38 0.17 255); }
.t-ai-engineering { --c: oklch(0.48 0.17 300); --tint: oklch(0.95 0.03 300); --chip: oklch(0.38 0.17 300); }
.t-system-design { --c: oklch(0.50 0.13 50); --tint: oklch(0.95 0.04 60); --chip: oklch(0.40 0.12 50); }
.t-papers { --c: oklch(0.46 0.09 195); --tint: oklch(0.95 0.03 195); --chip: oklch(0.36 0.09 195); }

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-padding-top: 16px; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 400 16px/1.5 var(--body); overflow-x: clip; }
[hidden] { display: none !important; }
h1, h2, h3 { font-family: var(--display); font-weight: 700; letter-spacing: -0.02em; margin: 0; text-wrap: balance; color: var(--ink); }
h2 { font-size: clamp(24px, 3.4vw, 32px); line-height: 1.12; }
h3 { font-size: 20px; line-height: 1.2; font-weight: 600; }
p { margin: 0; text-wrap: pretty; }
ul, ol { margin: 0; padding: 0; list-style: none; }
a { color: inherit; }
button { font: inherit; color: inherit; cursor: pointer; }
code, kbd { font-family: var(--mono); font-weight: 500; }
:focus-visible { outline: 2px solid var(--ink); outline-offset: 2px; }
.dark :focus-visible, .interview :focus-visible, .code-block:focus-visible { outline-color: #fff; }
.h1-home { font-size: clamp(40px, 8vw, 60px); line-height: 1.02; }
.h1-track { font-size: clamp(36px, 6.5vw, 48px); line-height: 1.05; }
.h1-lesson { font-size: clamp(32px, 6vw, 44px); line-height: 1.06; }
.lead { font-size: clamp(18px, 2vw, 19px); line-height: 1.45; color: var(--muted); max-width: 620px; }
.eyebrow, .mono-mini { font: 500 12px/1.4 var(--mono); text-transform: uppercase; letter-spacing: .04em; color: var(--muted); }
.note { font-size: 14px; color: var(--muted); }
.note a { display: inline-flex; align-items: center; min-height: 44px; }
.sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip-path: inset(50%); white-space: nowrap; }
.skip { position: absolute; left: 8px; top: -60px; background: var(--ink); color: #fff; padding: 10px 14px; border-radius: var(--radius-control); z-index: 10; }
.skip:focus { top: 8px; }

.page, .page-wide { width: 100%; margin-inline: auto; padding-inline: var(--gutter); }
.page { max-width: calc(1160px + 2 * var(--gutter)); }
.page-wide { max-width: calc(1280px + 2 * var(--gutter)); }
.panel { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius-card); }
.card-grid { display: grid; gap: 16px; grid-template-columns: repeat(auto-fit, minmax(min(250px, 100%), 1fr)); }

/* Header */
.site-head { background: var(--surface); border-bottom: 1px solid var(--line); }
.head-inner { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 20px; min-height: 68px; padding-block: 12px; }
.brand { display: inline-flex; align-items: center; gap: 10px; min-height: 44px; font: 700 18px/1 var(--display); letter-spacing: -0.01em; text-decoration: none; margin-right: auto; }
.logo { flex: none; }
.links { display: flex; flex-wrap: wrap; gap: 4px 20px; order: 1; }
.links a { display: inline-flex; align-items: center; min-height: 44px; font-weight: 500; text-decoration: none; }
.links a:hover { text-decoration: underline; text-underline-offset: 4px; }
.tabs { display: flex; flex-wrap: wrap; gap: 4px; order: 1; }
.tabs a { display: inline-flex; align-items: center; min-height: 44px; padding-inline: 12px; border-radius: var(--radius-control); font-weight: 500; text-decoration: none; }
.tabs a:hover { background: var(--line-soft); }
.tabs a.active { background: var(--tint); color: var(--chip); font-weight: 600; }
.search-btn { order: 2; display: inline-flex; align-items: center; gap: 8px; height: 44px; padding-inline: 12px; background: var(--surface); border: 1px solid var(--line-strong); border-radius: var(--radius-control); color: var(--muted); font-weight: 500; }
.search-btn:hover { border-color: var(--ink); color: var(--ink); }
.search-btn kbd { font-size: 12px; padding: 2px 6px; border-radius: 6px; background: var(--line-soft); color: var(--muted); }
html:not(.has-js) .search-btn { display: none; }
@media (pointer: coarse) { .search-btn kbd { display: none; } }

/* Chips and buttons */
.chip { display: inline-flex; align-items: center; min-height: 26px; padding: 3px 10px; border-radius: var(--radius-chip); font: 500 12px/1.3 var(--mono); letter-spacing: .04em; text-transform: uppercase; background: var(--line-soft); color: var(--muted); text-decoration: none; }
.type-track, .type-lab, .track-num { background: var(--tint); color: var(--chip); }
.type-interview { background: var(--ink); color: #fff; }
.chip-link { position: relative; background: var(--tint); color: var(--chip); text-transform: none; letter-spacing: 0; font: 500 13px/1.3 var(--body); text-decoration: underline; text-underline-offset: 2px; }
.chip-link::after { content: ""; position: absolute; inset: -9px -2px; }
.chip-road { min-height: 44px; padding-inline: 14px; background: var(--tint); color: var(--chip); font: 600 14px/1.2 var(--body); letter-spacing: 0; text-transform: none; }
.chip-road:hover, .chip-link:hover { outline: 1px solid var(--c); }
.btn { display: inline-flex; flex-direction: column; justify-content: center; align-items: flex-start; min-height: 48px; padding: 8px 18px; border-radius: var(--radius-control); border: 1px solid transparent; font-weight: 600; line-height: 1.25; text-decoration: none; }
.btn-primary { background: var(--ink); color: #fff; }
.btn-primary:hover { background: #2A2F3A; }
.btn-secondary { background: transparent; border-color: var(--ink); color: var(--ink); }
.btn-secondary:hover { background: var(--line-soft); }
.btn-track { background: var(--c); color: #fff; }
.btn-track:hover { background: var(--chip); }
.btn-row { display: flex; flex-wrap: wrap; gap: 12px; }
.link-btn { background: none; border: 0; padding: 0; min-height: 44px; color: var(--muted); font-weight: 500; text-decoration: underline; text-underline-offset: 3px; }
.link-btn:hover { color: var(--ink); }
.link-btn:disabled { color: var(--muted); text-decoration: none; cursor: default; }

/* Status dot */
.dot { flex: none; display: inline-block; width: 12px; height: 12px; border-radius: 50%; border: 1.5px solid var(--line-strong); background: transparent; }
.dot svg { display: none; width: 100%; height: 100%; }
.dot[data-state="in-progress"] { background: var(--c); border-color: var(--c); }
.dot[data-state="done"] { width: 16px; height: 16px; margin: -2px; background: var(--c); border-color: var(--c); }
.dot[data-state="done"] svg { display: block; }

/* Home */
.hero { display: grid; gap: 40px; grid-template-columns: repeat(auto-fit, minmax(min(420px, 100%), 1fr)); align-items: center; padding-block: clamp(36px, 7vw, 80px) clamp(32px, 5vw, 56px); }
.hero-copy { display: grid; gap: 20px; justify-items: start; }
.preview { display: grid; gap: 12px; justify-items: start; padding: clamp(20px, 3vw, 32px); box-shadow: 0 18px 40px -24px rgb(17 20 27 / .28); }
.preview h2 { font-size: clamp(24px, 3vw, 28px); }
.preview p { color: var(--muted); }
.tokens { display: flex; flex-wrap: wrap; gap: 8px; padding-block: 8px; }
.token { display: inline-flex; align-items: center; min-height: 44px; padding: 6px 14px; border: 1px solid var(--line); border-radius: var(--radius-control); font: 500 15px/1.2 var(--mono); color: var(--ink); background: color-mix(in oklch, var(--c) calc(var(--w) * 100%), white); }
.token.is-top { color: #fff; border-color: var(--c); }
.token.selected { outline: 2px solid var(--ink); outline-offset: 2px; }
button.token:hover { border-color: var(--ink); }
.pills { display: flex; flex-wrap: wrap; gap: 6px; }
.tag { padding: 4px 11px; border-radius: var(--radius-chip); background: var(--line-soft); font-size: 13px; font-weight: 500; color: var(--muted); }
.section { padding-block: clamp(28px, 4.5vw, 44px); }
.section > h2 { margin-bottom: 8px; }
.section-lead { color: var(--muted); max-width: 620px; }
.section > .section-lead { margin-bottom: 20px; }
.section > h2 + .card-grid { margin-top: 20px; }
.start { display: grid; gap: 8px; align-content: start; padding: 22px; text-decoration: none; }
.start p { color: var(--muted); }
a.panel:hover { border-color: var(--ink); }
.dark { background: var(--ink); border-color: var(--ink); color: #fff; }
.dark h3 { color: #fff; }
.dark p, .dark .eyebrow { color: var(--on-dark); }
.track-card { display: flex; flex-direction: column; gap: 10px; padding: 20px; text-decoration: none; }
.track-card:hover { border-color: var(--c); }
.track-top { display: flex; align-items: center; justify-content: space-between; gap: 8px; flex-wrap: wrap; }
.status-note { font-size: 13px; font-weight: 500; color: var(--muted); }
.track-card h3 { font-size: 24px; font-weight: 700; color: var(--chip); }
.track-card > p { color: var(--muted); }
.track-card ul { margin-top: 4px; border-top: 1px solid var(--line-soft); }
.track-card li { padding-block: 8px; border-bottom: 1px solid var(--line-soft); font-size: 14px; }
.track-card li:last-child { border-bottom: 0; padding-bottom: 0; }
.grid-tiles { display: grid; gap: 12px; grid-template-columns: repeat(auto-fit, minmax(min(250px, 100%), 1fr)); }
.tile { display: grid; gap: 8px; align-content: start; padding: 18px; }
.tile h3 { font-size: 18px; }
.tile p { font-size: 14px; color: var(--muted); }
.tile.dark p { color: var(--on-dark); }
.road-card { display: grid; gap: 18px; padding: clamp(20px, 3vw, 32px); }
.road { display: flex; flex-wrap: wrap; gap: 10px 8px; align-items: center; }
.road li { display: inline-flex; align-items: center; gap: 8px; }
.road li + li::before { content: "→"; color: var(--muted); }

/* Track */
.band { background: var(--surface); border-bottom: 1px solid var(--line); }
.band-inner { display: grid; gap: 28px; grid-template-columns: repeat(auto-fit, minmax(min(320px, 100%), 1fr)); align-items: start; padding-block: clamp(14px, 2.5vw, 24px) clamp(24px, 4vw, 40px); }
.band-inner > div:first-child { display: grid; gap: 12px; justify-items: start; }
.crumbs { display: flex; flex-wrap: wrap; align-items: center; gap: 0 8px; font-size: 14px; color: var(--muted); }
.crumbs a { display: inline-flex; align-items: center; min-height: 44px; min-width: 44px; text-underline-offset: 3px; }
.crumbs b { font-weight: 600; color: var(--ink); padding-block: 4px; }
.know { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; padding-top: 6px; font-size: 14px; font-weight: 500; color: var(--muted); }
.continue { display: grid; gap: 10px; padding: 22px; }
.continue h2 { font-size: 22px; }
.progress { height: 8px; background: var(--line-soft); border-radius: 999px; overflow: hidden; }
.progress i { display: block; height: 100%; width: 0; background: var(--c); }
.progress-note { font-size: 14px; color: var(--muted); }
.continue .btn { justify-self: start; }
.modules { display: grid; gap: 20px; padding-block: 28px 56px; }
.module { overflow: hidden; }
.module header { display: grid; gap: 4px; padding: 20px 22px 16px; border-bottom: 1px solid var(--line); }
.module h2 { font-size: 24px; }
.module header p:last-child { color: var(--muted); }
.row { display: grid; grid-template-columns: 16px minmax(0, 1fr) auto 54px; gap: 14px; align-items: center; min-height: 56px; padding: 10px 22px; text-decoration: none; }
.rows li + li { border-top: 1px solid var(--line-soft); }
.row:hover { background: var(--tint); }
.row-title { font-weight: 500; }
.mins { font-size: 14px; color: var(--muted); white-space: nowrap; }
.row .mins { text-align: right; }
.next-track { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 16px; padding: 22px; }
.next-track h2 { font-size: 24px; }
.next-track p:last-child { color: var(--muted); }
@media (max-width: 560px) {
  .row { grid-template-columns: 16px minmax(0, 1fr) auto; row-gap: 6px; padding-inline: 16px; }
  .row-title { grid-column: 2 / -1; }
  .row .chip { grid-column: 2; justify-self: start; }
  .module header { padding-inline: 16px; }
}

/* Lesson shell */
.lesson-grid { display: grid; grid-template-columns: 250px minmax(0, 1fr) 200px; gap: 36px; align-items: start; padding-block: 20px 56px; }
.contents, .rail { position: sticky; top: 16px; max-height: calc(100vh - 32px); overflow-y: auto; }
.contents-box > summary { font: 500 12px/1.4 var(--mono); text-transform: uppercase; letter-spacing: .04em; color: var(--chip); min-height: 32px; list-style: none; padding: 4px; }
.contents-box > summary::-webkit-details-marker { display: none; }
.mod { border-top: 1px solid var(--line); }
.mod > summary { display: flex; align-items: center; justify-content: space-between; gap: 8px; min-height: 44px; font-weight: 600; font-size: 14px; cursor: pointer; padding-inline: 4px; list-style: none; }
.mod > summary::-webkit-details-marker { display: none; }
.mod > summary::after { content: ""; flex: none; width: 7px; height: 7px; margin-right: 4px; border-right: 1.5px solid var(--muted); border-bottom: 1.5px solid var(--muted); transform: translateY(-2px) rotate(45deg); transition: transform .15s; }
.mod[open] > summary::after { transform: translateY(2px) rotate(-135deg); }
@media (prefers-reduced-motion: reduce) { .mod > summary::after { transition: none; } }
.mod ol { padding-bottom: 8px; }
.mod a { display: flex; align-items: center; gap: 10px; min-height: 44px; padding: 7px 8px; border-radius: 8px; font-size: 14px; line-height: 1.3; text-decoration: none; }
.mod a:hover { background: var(--line-soft); }
.mod a.current { background: var(--tint); color: var(--chip); font-weight: 600; }
.lesson { display: grid; gap: 16px; min-width: 0; }
.lesson > .crumbs { margin-top: -8px; }
.lesson-meta { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 10px; }
.before { font-size: 14px; color: var(--muted); }
.depth { display: flex; flex-wrap: wrap; gap: 0; width: fit-content; max-width: 100%; border: 1px solid var(--line-strong); border-radius: var(--radius-control); background: var(--surface); overflow: hidden; }
.depth button { min-height: 44px; padding-inline: 16px; background: transparent; border: 0; font-weight: 500; }
.depth button + button { border-left: 1px solid var(--line-strong); }
.depth button:hover { background: var(--line-soft); }
.depth button[aria-pressed="true"] { background: var(--ink); color: #fff; font-weight: 600; }
.depth button:focus-visible { outline-offset: -4px; }
.depth button[aria-pressed="true"]:focus-visible { outline-color: #fff; }
html:not(.has-js) .depth { display: none; }
.block { display: grid; gap: 14px; padding: clamp(18px, 2.6vw, 26px); min-width: 0; }
.block h2 { font-size: 24px; }
.idea > p:last-child { font-size: 18px; line-height: 1.5; max-width: 620px; }
.block > p { max-width: 620px; }
.mono-box { padding: 16px; background: var(--bg); border: 1px solid var(--line); border-radius: var(--radius-control); font: 500 14px/1.7 var(--mono); white-space: pre-wrap; overflow-wrap: anywhere; }
.explain { display: grid; gap: 8px; max-width: 620px; }
.explain li { position: relative; padding-left: 18px; }
.explain li::before { content: ""; position: absolute; left: 2px; top: .62em; width: 6px; height: 6px; border-radius: 50%; background: var(--c); }
.explain code, .note code { padding: 1px 5px; border-radius: 5px; background: var(--line-soft); font-size: .9em; }
.code-block { margin: 0; padding: 18px; background: var(--ink); color: #E8EBF1; border-radius: var(--radius-control); font: 500 13px/1.65 var(--mono); overflow-x: auto; }
.code-block code { font: inherit; }
.stages { display: grid; gap: 10px; grid-template-columns: repeat(auto-fit, minmax(min(130px, 100%), 1fr)); }
.stages li { display: grid; gap: 4px; align-content: start; padding: 14px; background: var(--tint); border-radius: var(--radius-control); }
.stages .mono-num { font: 500 12px/1 var(--mono); color: var(--chip); }
.stages b { font-weight: 600; line-height: 1.25; }
.stages li > span:last-child { font-size: 14px; color: var(--muted); }
.dashed { padding: 14px; border: 1.5px dashed var(--line-strong); border-radius: var(--radius-control); font-size: 15px; }
.widget { display: grid; gap: 10px; }
.widget .tokens { padding-top: 2px; }
.widget-caption { font-size: 15px; }
.meters { display: grid; gap: 6px; }
.bar-row { display: grid; grid-template-columns: 62px minmax(0, 1fr) 44px; gap: 10px; align-items: center; font: 500 13px/1.3 var(--mono); }
.meter { height: 14px; background: var(--line-soft); border-radius: 4px; overflow: hidden; }
.meter i { display: block; height: 100%; background: var(--c); transition: width .2s ease; }
.bar-pct { text-align: right; }
.interview { display: grid; gap: 12px; justify-items: start; padding: clamp(20px, 3vw, 30px); background: var(--ink); color: #fff; border-radius: var(--radius-card); }
.interview .eyebrow { color: var(--on-dark); }
.interview h2 { color: #fff; font-size: clamp(22px, 3vw, 28px); }
.interview .say-first { color: var(--on-dark); }
.btn-reveal { background: #fff; color: var(--ink); align-items: center; }
.btn-reveal:hover { background: var(--line); }
.answer { padding-top: 12px; border-top: 1px solid #3A404D; max-width: 620px; font-size: 17px; }
.has-js .answer:not(.open) { display: none; }
html:not(.has-js) [data-reveal] { display: none; }
.mark-done { display: flex; justify-content: flex-end; margin-top: -6px; }
.prev-next { display: flex; flex-wrap: wrap; justify-content: space-between; align-items: center; gap: 12px; padding-top: 12px; border-top: 1px solid var(--line); }
.prev-next .btn { flex: 1 1 220px; max-width: 340px; }
.prev-next .btn-track { margin-left: auto; }
.pn-label { font: 500 11px/1.5 var(--mono); text-transform: uppercase; letter-spacing: .04em; opacity: .85; }
.first-note { flex: 1 1 220px; font-size: 14px; color: var(--muted); }
.rail { display: grid; gap: 22px; }
.page-toc ul, .related ul { display: grid; margin-top: 6px; }
.page-toc a { display: flex; align-items: center; min-height: 44px; padding-block: 4px; font-size: 14px; line-height: 1.3; color: var(--muted); text-decoration: none; }
.page-toc a:hover { color: var(--ink); text-decoration: underline; }
.page-toc a[aria-current] { color: var(--ink); font-weight: 600; }
.related { padding: 14px; background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius-card); }
.related li { display: grid; padding-block: 8px; }
.related li + li { border-top: 1px solid var(--line-soft); }
.related .mono-mini { font-size: 11px; }
.related a { display: flex; align-items: center; min-height: 44px; font-size: 14px; font-weight: 500; line-height: 1.3; padding-block: 4px; text-underline-offset: 2px; }
@media (max-width: 1140px) {
  .lesson-grid { grid-template-columns: 230px minmax(0, 1fr); }
  .rail { grid-column: 2; position: static; max-height: none; overflow: visible; }
}
@media (max-width: 820px) {
  .lesson-grid { grid-template-columns: minmax(0, 1fr); gap: 20px; padding-top: 12px; }
  .contents { position: static; max-height: none; overflow: visible; background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius-control); padding: 0 12px; }
  .contents-box > summary { display: flex; align-items: center; justify-content: space-between; min-height: 44px; cursor: pointer; padding-inline: 0; }
  .contents-box > summary::after { content: ""; width: 7px; height: 7px; margin-right: 4px; border-right: 1.5px solid var(--muted); border-bottom: 1.5px solid var(--muted); transform: translateY(-2px) rotate(45deg); }
  .contents-box[open] > summary::after { transform: translateY(2px) rotate(-135deg); }
  .rail { grid-column: 1; }
  .depth { display: grid; grid-template-columns: repeat(auto-fit, minmax(90px, 1fr)); width: 100%; }
  .depth button { padding-inline: 8px; }
  .prev-next .btn { max-width: none; }
}

/* Search */
.search { width: min(620px, calc(100vw - 24px)); max-height: min(70vh, 620px); padding: 0; margin: 10vh auto auto; border: 1px solid var(--line); border-radius: var(--radius-card); background: var(--surface); color: var(--ink); overflow: hidden; }
.search[open] { display: flex; flex-direction: column; }
.search::backdrop { background: rgb(17 20 27 / .45); }
.search-top { display: flex; gap: 8px; align-items: center; padding: 12px; border-bottom: 1px solid var(--line); }
.search input { flex: 1; min-width: 0; height: 44px; padding-inline: 12px; font: 400 16px var(--body); color: var(--ink); background: var(--bg); border: 1px solid var(--line-strong); border-radius: var(--radius-control); }
.btn-close { height: 44px; padding-inline: 12px; background: none; border: 1px solid var(--line-strong); border-radius: var(--radius-control); font-weight: 500; }
.search-results { overflow-y: auto; padding: 12px; display: grid; gap: 14px; }
.search-group { display: grid; gap: 4px; }
.search-group > .chip { justify-self: start; }
.search-hit { display: grid; min-height: 52px; padding: 8px 10px; border-radius: 8px; text-decoration: none; }
.search-hit:hover, .search-hit:focus-visible { background: var(--tint); }
.search-hit b { font-weight: 600; }
.search-hit span { font-size: 13px; color: var(--muted); }
.search-empty { color: var(--muted); padding: 8px; }

/* Moved lessons */
.lesson > .interview + .interview { margin-top: -2px; }
.interview.practice h2 { font-size: clamp(19px, 2.4vw, 22px); line-height: 1.25; letter-spacing: -0.01em; font-weight: 600; text-wrap: pretty; }
.answer ol, .answer ul { list-style: decimal; padding-left: 22px; margin-bottom: 10px; }
.answer ul { list-style: disc; }
.answer li + li { margin-top: 6px; }
.answer .small { color: var(--on-dark); font-size: 15px; }
.answer .ans b { font-weight: 700; }
.part-title { font-size: 28px; margin-top: 12px; }
.part-title:first-child { margin-top: 0; }
.module h3 { font-size: 24px; font-weight: 700; }
.contents-part { padding: 12px 4px 6px; font: 500 12px/1.4 var(--mono); text-transform: uppercase; letter-spacing: .04em; color: var(--muted); }
.answer h3 { margin: 18px 0 6px; color: #fff; font-size: 18px; }
.answer h3:first-child { margin-top: 0; }
.answer p { margin-bottom: 10px; }
.answer a { color: #fff; }
.answer .say30 { font-size: 17px; }
.answer details.qa { border-top: 1px solid #3A404D; }
.answer details.qa summary { display: flex; align-items: center; min-height: 44px; padding-block: 8px; font-weight: 600; cursor: pointer; }
.answer details.qa p { color: var(--on-dark); }
.idea-text { font-size: 17px; line-height: 1.55; }
.idea-text .small { display: block; margin-top: 10px; font-size: 15px; color: var(--muted); }

/* Seven-section lessons */
.sit-lead { color: var(--muted); max-width: 620px; }
.sit-q { margin: 0; padding-left: 16px; border-left: 3px solid var(--c); font: 600 clamp(21px, 2.8vw, 26px)/1.22 var(--display); letter-spacing: -0.015em; text-wrap: balance; }
.sit-more { color: var(--muted); font-size: 15px; display: grid; grid-template-columns: minmax(0, 1fr); gap: 10px; padding-top: 4px; border-top: 1px solid var(--line-soft); }
.idea-analogy { font-size: 18px; line-height: 1.5; max-width: 620px; }
.picture { margin: 0; display: grid; gap: 8px; }
.picture svg { width: 100%; max-width: 520px; height: auto; display: block; }
.picture figcaption { font-size: 14px; color: var(--muted); max-width: 620px; }
.lesson-tabs { position: sticky; top: 0; z-index: 5; display: grid; grid-auto-flow: column; grid-auto-columns: minmax(0, 1fr); background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius-control); overflow: hidden; }
.lesson-tabs button { min-height: 48px; padding: 6px 4px; background: none; border: 0; font-size: 15px; font-weight: 500; line-height: 1.15; color: var(--muted); }
.lesson-tabs button + button { border-left: 1px solid var(--line); }
.lesson-tabs button:hover { background: var(--line-soft); color: var(--ink); }
.lesson-tabs button[aria-selected="true"] { background: var(--ink); color: #fff; font-weight: 600; }
.lesson-tabs button:focus-visible { outline-offset: -4px; }
.lesson-tabs button[aria-selected="true"]:focus-visible { outline-color: #fff; }
html:not(.has-js) .lesson-tabs, html:not(.has-js) [data-tab-go] { display: none; }
.tab-panel { display: grid; grid-template-columns: minmax(0, 1fr); gap: 16px; min-width: 0; outline: none; scroll-margin-top: 60px; }
.tab-panel .sec { scroll-margin-top: 60px; }
.tab-panel > .sec, .tab-panel > .idea, .lx .tab-panel > .sec, .lx .tab-panel > .idea { margin-top: 0; }
.panel-next { justify-self: end; align-items: center; }
.lx .btn-track { color: #fff; font-weight: 600; }
.lx .tab-panel section.ch { margin-top: 0; scroll-margin-top: 60px; }
.lx .tab-panel .sec > section.ch + section.ch { margin-top: 4px; }
@media (max-width: 480px) { .lesson-tabs button { font-size: 13px; } }
.sec { display: grid; grid-template-columns: minmax(0, 1fr); gap: 12px; margin-top: 16px; min-width: 0; }
.lesson > .sec { margin-top: 0; }
.sec-title { font-size: clamp(24px, 3vw, 30px); padding-top: 8px; }
.play-try, .play-why { max-width: 620px; }
.play-why { padding: 12px 16px; background: var(--tint); color: var(--chip); border-radius: var(--radius-control); max-width: none; }
.say-card { margin-top: 8px; background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius-card); overflow: hidden; scroll-margin-top: 12px; }
.say-head { display: grid; gap: 8px; padding: clamp(20px, 3vw, 28px); background: var(--ink); }
.say-head .eyebrow { color: var(--on-dark); }
.say-head h2 { color: #fff; font-size: clamp(22px, 3vw, 28px); line-height: 1.16; }
.say-stepper { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); border-bottom: 1px solid var(--line); }
.say-stepper button { display: flex; align-items: center; justify-content: center; gap: 8px; width: 100%; min-height: 52px; padding: 6px 4px; background: none; border: 0; font-size: 14px; font-weight: 500; color: var(--muted); }
.say-stepper button:disabled { cursor: default; }
.say-stepper button:not(:disabled):hover { background: var(--line-soft); }
.say-stepper button:focus-visible { outline-offset: -4px; }
.say-dot { flex: none; display: grid; place-items: center; width: 24px; height: 24px; border: 1.5px solid var(--line-strong); border-radius: 50%; font: 500 12px/1 var(--mono); background: var(--surface); }
.say-stepper [data-state="done"] .say-dot { border-color: var(--c); color: var(--chip); background: var(--tint); }
.say-stepper [data-state="current"] button { color: var(--ink); font-weight: 600; box-shadow: inset 0 -2px 0 var(--c); }
.say-stepper [data-state="current"] .say-dot { border-color: var(--c); background: var(--c); color: #fff; }
.say-body { padding: clamp(18px, 3vw, 26px); }
.say-step { display: grid; grid-template-columns: minmax(0, 1fr); gap: 14px; outline: none; }
.say-step + .say-step { margin-top: 28px; }
.has-js .say-step + .say-step { margin-top: 0; }
.say-step h3 { font-size: 21px; font-weight: 700; }
.say-hint { color: var(--muted); max-width: 620px; }
.say-actions { display: flex; flex-wrap: wrap; align-items: center; gap: 10px 16px; }
.say-actions .btn { align-items: center; }
.checks { display: grid; gap: 8px; }
.checks label { display: flex; gap: 12px; align-items: flex-start; min-height: 48px; padding: 12px 14px; border: 1px solid var(--line); border-radius: var(--radius-control); line-height: 1.4; cursor: pointer; }
.checks label:hover { border-color: var(--line-strong); background: var(--bg); }
.checks label:has(input:checked) { border-color: var(--c); background: var(--tint); }
.checks input { flex: none; width: 20px; height: 20px; margin: 1px 0 0; accent-color: var(--c); }
.check-meter { display: flex; align-items: center; gap: 12px; }
.check-meter .meter { flex: 1; height: 6px; background: var(--line-soft); border-radius: 99px; overflow: hidden; }
.check-meter i { display: block; height: 100%; width: 0; background: var(--c); transition: width .15s ease; }
.check-count { font: 500 12px/1.4 var(--mono); color: var(--muted); white-space: nowrap; }
.fu { display: grid; grid-template-columns: minmax(0, 1fr); gap: 10px; }
.fu + .fu { margin-top: 24px; }
.has-js .fu + .fu { margin-top: 0; }
.fu-q { font: 600 clamp(19px, 2.4vw, 22px)/1.25 var(--display); letter-spacing: -0.01em; text-wrap: balance; }
.say-card .answer { padding: 14px 16px; border: 0; border-radius: var(--radius-control); background: var(--tint); color: var(--ink); font-size: 16px; max-width: none; }
.say-card .answer p { margin: 0; }
.say-card .answer a { color: inherit; }
.say-score { padding: 10px 14px; border-radius: var(--radius-control); background: var(--tint); color: var(--chip); font-weight: 600; }
.say-final h3 { margin: 0; }
.say-final .say30 { font-size: 17px; line-height: 1.55; max-width: 640px; }
.say-more { border-top: 1px solid var(--line); }
.say-more > summary { display: flex; align-items: center; min-height: 48px; font-weight: 600; cursor: pointer; }
.say-more h3 { margin: 12px 0 6px; font-size: 17px; font-weight: 600; }
.say-more p { max-width: 640px; margin-bottom: 8px; }
.say-more ul, .say-more ol { list-style: disc; padding-left: 22px; }
html:not(.has-js) .say-stepper, html:not(.has-js) [data-say-go], html:not(.has-js) [data-next-fu] { display: none; }
@media (max-width: 480px) { .say-stepper button { flex-direction: column; gap: 3px; font-size: 12px; min-height: 60px; } }
.lx .idea, .lx .sec { margin-top: 16px; }
h2.eyebrow, .lx h2.eyebrow { font: 500 12px/1.4 var(--mono); letter-spacing: .04em; text-transform: uppercase; color: var(--muted); }
.lx .sec-title { font-size: clamp(24px, 3vw, 30px); }
.lx .sec section.ch { margin-top: 0; }
.lx .sit-more section.ch { padding: 0; margin: 0; border: 0; background: none; }
.lx .sit-more h3 { font-size: 17px; margin: 0 0 6px; }
.lx .sit-more p { margin: 0; }
.lx .sec .ch h3 { margin: 0 0 12px; font-size: 22px; font-weight: 700; line-height: 1.2; }
.lx .sec .ch h4 { margin: 22px 0 8px; font-size: 18px; }
.lx #summary .small { display: block; margin-top: 10px; }

/* Practice pages */
.say-stepper.many { display: flex; flex-wrap: wrap; }
.say-stepper.many li { flex: 1 0 44px; }
.practice-card .say-head h2 { font-size: clamp(20px, 2.6vw, 24px); line-height: 1.25; font-weight: 600; letter-spacing: -0.01em; text-wrap: pretty; }
.pq { outline: none; }
.pq + .pq { border-top: 1px solid var(--line); }
.has-js .pq + .pq { border-top: 0; }
.say-card .answer .ans { margin-bottom: 10px; }
.say-card .answer ol { margin: 0 0 10px; }
.say-card .answer .small { color: var(--muted); }
html:not(.has-js) .say-stepper.many, html:not(.has-js) [data-pq-go], html:not(.has-js) [data-pq-finish] { display: none; }

/* Paper lessons */
.paper-meta { font-size: 14px; color: var(--muted); }
.paper-tldr { font-size: 17px; line-height: 1.55; max-width: 640px; }
.paper-tldr .small { display: block; margin-top: 10px; font-size: 15px; color: var(--muted); }
.lx .paper-card .legend { margin-top: 0; }
.lx .tab-panel > section, .lx .tab-panel .sec > section { margin-top: 0; }
.lx .tab-panel .sec > section.ch h4 { margin: 18px 0 8px; font-size: 18px; }
.lx .picture .diagram { margin: 0; }

/* Footer */
.site-foot { background: var(--surface); border-top: 1px solid var(--line); margin-top: 16px; }
.foot-inner { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 6px 20px; padding-block: 20px; font-size: 14px; color: var(--muted); }
.foot-inner span:first-child { font-weight: 600; color: var(--ink); }

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { transition: none !important; animation: none !important; scroll-behavior: auto !important; }
}

.hero-roadmaps { padding-block: clamp(40px, 7vw, 72px); }
.hero-roadmaps .lead { margin-bottom: 28px; }
.foot-inner a { color: inherit; }