/* ---------- tokens ---------- */
:root {
  --bg: #0e1117; --bg-2: #141922; --bg-3: #1b2230; --line: #263043;
  --fg: #e5e9f0; --fg-dim: #97a3b6; --fg-faint: #6b7789;
  --accent: #6f9dff; --accent-2: #8b7bff; --accent-soft: rgba(111,157,255,.14);
  --ok: #46c08d; --warn: #e6b45e; --danger: #ef6f6f; --info: #56b6c2;
  --radius: 12px; --radius-s: 8px;
  --mono: ui-monospace, "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, Roboto, sans-serif;
  --sidebar-w: 280px; --topbar-h: 58px; --measure: 900px; --lesson-w: 880px; --rail-w: 272px;
  --shadow: 0 12px 32px rgba(0,0,0,.35);
}
:root[data-theme="light"] {
  --bg: #fbfbfd; --bg-2: #ffffff; --bg-3: #f2f4f8; --line: #e0e4ec;
  --fg: #1a1f2b; --fg-dim: #5a6577; --fg-faint: #8b95a6;
  --accent: #2f5fd8; --accent-2: #6b4fd8; --accent-soft: rgba(47,95,216,.10);
  --ok: #17835c; --warn: #9a6b12; --danger: #c4383c; --info: #1b7f8c;
  --shadow: 0 10px 28px rgba(20,30,60,.10);
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }
html { scroll-behavior: smooth; scroll-padding-top: calc(var(--topbar-h) + 16px); }
body {
  margin: 0; background: var(--bg); color: var(--fg);
  font-family: var(--sans); font-size: 17px; line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
kbd {
  font-family: var(--mono); font-size: 11px; background: var(--bg-3);
  border: 1px solid var(--line); border-radius: 5px; padding: 1px 5px; color: var(--fg-dim);
}

/* ---------- topbar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 40; height: var(--topbar-h);
  display: flex; align-items: center; gap: 12px; padding: 0 14px;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(12px); border-bottom: 1px solid var(--line);
}
.brand { display: flex; align-items: center; gap: 9px; color: var(--fg); font-weight: 650; }
.brand:hover { text-decoration: none; }
.brand-mark {
  display: grid; place-items: center; width: 26px; height: 26px; border-radius: 7px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #fff; font-size: 12px; font-weight: 800;
}
.brand-text { font-size: 14.5px; letter-spacing: -.01em; }
.icon-btn {
  background: none; border: 1px solid transparent; color: var(--fg-dim);
  font-size: 17px; cursor: pointer; padding: 6px 9px; border-radius: var(--radius-s);
}
.icon-btn:hover { background: var(--bg-3); color: var(--fg); }
#menu-btn { display: none; }
.search-trigger {
  flex: 1; max-width: 420px; margin: 0 auto; display: flex; align-items: center; justify-content: space-between;
  gap: 10px; padding: 6px 10px; background: var(--bg-2); border: 1px solid var(--line);
  border-radius: 999px; color: var(--fg-faint); font-size: 13px; cursor: pointer; font-family: inherit;
}
.search-trigger:hover { border-color: var(--accent); color: var(--fg-dim); }
.topbar-right { display: flex; align-items: center; gap: 4px; margin-left: auto; }
.ghost-btn {
  font-size: 13px; color: var(--fg-dim); padding: 6px 10px; border-radius: var(--radius-s);
}
.ghost-btn:hover { background: var(--bg-3); color: var(--fg); text-decoration: none; }

/* ---------- layout ---------- */
.shell { display: flex; align-items: flex-start; }
.sidebar {
  position: sticky; top: var(--topbar-h); flex: 0 0 var(--sidebar-w); width: var(--sidebar-w);
  height: calc(100vh - var(--topbar-h)); overflow-y: auto; padding: 16px 10px 60px;
  border-right: 1px solid var(--line); background: var(--bg);
}
.sidebar::-webkit-scrollbar { width: 9px; }
.sidebar::-webkit-scrollbar-thumb { background: var(--line); border-radius: 9px; }
main { flex: 1; min-width: 0; }
.page { max-width: var(--measure); margin: 0 auto; padding: 40px 40px 120px; }
.page.home { max-width: 1180px; }
.scrim { display: none; }

/* ---------- sidebar nav ---------- */
.sidebar-progress { padding: 8px 10px 14px; border-bottom: 1px solid var(--line); margin-bottom: 10px; }
.sp-row { display: flex; justify-content: space-between; font-size: 12px; color: var(--fg-dim); margin-bottom: 7px; }
.sp-row strong { color: var(--fg); }
.sp-meta { font-size: 11.5px; color: var(--fg-faint); margin-top: 7px; }
.bar { height: 5px; background: var(--bg-3); border-radius: 99px; overflow: hidden; }
.bar i { display: block; height: 100%; background: linear-gradient(90deg, var(--accent), var(--accent-2)); transition: width .3s; }
.bar.big { height: 8px; }

.nav-phase summary {
  display: flex; align-items: center; gap: 8px; padding: 8px 10px; cursor: pointer;
  border-radius: var(--radius-s); font-size: 14.5px; list-style: none; color: var(--fg-dim);
}
.nav-phase summary::-webkit-details-marker { display: none; }
.nav-phase summary:hover { background: var(--bg-3); color: var(--fg); }
.nav-num { font-family: var(--mono); font-size: 10.5px; color: var(--fg-faint); }
.nav-title { flex: 1; font-weight: 550; }
.nav-count { font-family: var(--mono); font-size: 10.5px; color: var(--fg-faint); }
.nav-count.complete { color: var(--ok); }
.nav-phase[open] > summary { color: var(--fg); }
.nav-phase ul { list-style: none; margin: 0 0 8px; padding: 0 0 0 10px; border-left: 1px solid var(--line); margin-left: 18px; }
.nav-phase li a {
  display: flex; gap: 7px; align-items: baseline; padding: 5px 9px; border-radius: 6px;
  font-size: 14px; color: var(--fg-dim); line-height: 1.4;
}
.nav-phase li a:hover { background: var(--bg-3); color: var(--fg); text-decoration: none; }
.nav-phase li a.active { background: var(--accent-soft); color: var(--accent); font-weight: 600; }
.nav-phase li a.done { color: var(--fg-faint); }
.tick { width: 11px; flex: none; font-size: 10px; color: var(--ok); }

/* ---------- typography ---------- */
h1 { font-size: 36px; line-height: 1.18; letter-spacing: -.025em; margin: 0 0 12px; }
h2 { font-size: 26px; line-height: 1.3; margin: 44px 0 14px; letter-spacing: -.015em; scroll-margin-top: 80px; }
h3 { font-size: 19px; margin: 30px 0 10px; scroll-margin-top: 80px; }
h4 { font-size: 14.5px; margin: 20px 0 6px; color: var(--fg-dim); text-transform: uppercase; letter-spacing: .05em; }
p, li { color: var(--fg); }
.lede { font-size: 19px; color: var(--fg-dim); line-height: 1.6; }
.eyebrow { font-size: 12px; text-transform: uppercase; letter-spacing: .1em; color: var(--accent); font-weight: 650; margin: 0 0 10px; }
.anchor { opacity: 0; margin-left: -.8em; padding-right: .3em; color: var(--fg-faint); font-weight: 400; }
h2:hover .anchor, h3:hover .anchor { opacity: 1; }
.prose ul, .prose ol { padding-left: 22px; }
.prose li { margin: 5px 0; }
.prose table { width: 100%; border-collapse: collapse; margin: 20px 0; font-size: 15.5px; }
.prose th, .prose td { border: 1px solid var(--line); padding: 8px 11px; text-align: left; vertical-align: top; }
.prose th { background: var(--bg-3); font-size: 13px; text-transform: uppercase; letter-spacing: .04em; color: var(--fg-dim); }
.prose blockquote {
  margin: 18px 0; padding: 2px 0 2px 16px; border-left: 3px solid var(--accent);
  color: var(--fg-dim); font-style: italic;
}
.prose hr { border: 0; border-top: 1px solid var(--line); margin: 34px 0; }
:not(pre) > code {
  font-family: var(--mono); font-size: .875em; background: var(--bg-3);
  border: 1px solid var(--line); border-radius: 5px; padding: .1em .35em; color: var(--fg);
}

/* ---------- code ---------- */
figure.code { margin: 16px 0; border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; background: var(--bg-2); }
figure.code figcaption {
  display: flex; justify-content: space-between; align-items: center;
  padding: 5px 12px; background: var(--bg-3); border-bottom: 1px solid var(--line);
}
.code-lang { font-family: var(--mono); font-size: 10.5px; text-transform: uppercase; letter-spacing: .08em; color: var(--fg-faint); }
.copy-btn {
  font-family: var(--sans); font-size: 11px; background: none; border: 1px solid var(--line);
  color: var(--fg-dim); padding: 2px 9px; border-radius: 6px; cursor: pointer;
}
.copy-btn:hover { border-color: var(--accent); color: var(--accent); }
pre { margin: 0; padding: 16px 20px; overflow-x: auto; }
pre code { font-family: var(--mono); font-size: 15px; line-height: 1.65; background: none; border: 0; padding: 0; }
.page > pre { background: var(--bg-2); border: 1px solid var(--line); border-radius: var(--radius); }

/* highlight.js tokens */
.hljs-keyword, .hljs-literal, .hljs-selector-tag { color: #c792ea; }
.hljs-string, .hljs-regexp { color: #a5d6a7; }
.hljs-title, .hljs-title.function_, .hljs-section { color: #82aaff; }
.hljs-title.class_, .hljs-type, .hljs-built_in { color: #ffcb6b; }
.hljs-number { color: #f78c6c; }
.hljs-comment, .hljs-quote { color: var(--fg-faint); font-style: italic; }
.hljs-meta, .hljs-meta .hljs-keyword { color: #89ddff; }
.hljs-attr, .hljs-attribute, .hljs-property { color: #80cbc4; }
.hljs-variable, .hljs-params { color: var(--fg); }
.hljs-symbol, .hljs-bullet, .hljs-doctag { color: #f07178; }
:root[data-theme="light"] .hljs-keyword, :root[data-theme="light"] .hljs-literal { color: #8250df; }
:root[data-theme="light"] .hljs-string { color: #0a7d40; }
:root[data-theme="light"] .hljs-title, :root[data-theme="light"] .hljs-title.function_ { color: #1f57c3; }
:root[data-theme="light"] .hljs-title.class_, :root[data-theme="light"] .hljs-type, :root[data-theme="light"] .hljs-built_in { color: #8a5a00; }
:root[data-theme="light"] .hljs-number { color: #b8500b; }
:root[data-theme="light"] .hljs-meta { color: #0e6d7d; }
:root[data-theme="light"] .hljs-attr { color: #116b62; }

/* ---------- ::: blocks ---------- */
.cx {
  margin: 22px 0; border: 1px solid var(--line); border-left: 3px solid var(--kind, var(--accent));
  border-radius: var(--radius); background: var(--bg-2); overflow: hidden;
}
.cx-head { display: flex; align-items: baseline; gap: 10px; padding: 14px 20px 0; flex-wrap: wrap; }
.cx-kind {
  font-size: 12px; font-weight: 750; text-transform: uppercase; letter-spacing: .09em;
  color: var(--kind, var(--accent)); white-space: nowrap;
}
.cx-title { font-size: 16px; font-weight: 600; color: var(--fg); }
.cx-body { padding: 4px 20px 18px; }
.cx-body > :first-child { margin-top: 8px; }
.cx-body > :last-child { margin-bottom: 0; }
.cx-body h3, .cx-body h4 { margin-top: 16px; }

.cx-exercise   { --kind: var(--ok); background: color-mix(in srgb, var(--ok) 6%, var(--bg-2)); }
.cx-challenge  { --kind: var(--accent-2); background: color-mix(in srgb, var(--accent-2) 7%, var(--bg-2)); }
.cx-project    { --kind: var(--accent); background: color-mix(in srgb, var(--accent) 8%, var(--bg-2)); }
.cx-checkpoint { --kind: var(--info); }
.cx-mistake    { --kind: var(--danger); }
.cx-warn       { --kind: var(--warn); }
.cx-debug      { --kind: var(--danger); background: color-mix(in srgb, var(--danger) 6%, var(--bg-2)); }
.cx-predict    { --kind: var(--warn); }
.cx-refactor   { --kind: var(--accent-2); }
.cx-design     { --kind: var(--info); }
.cx-why        { --kind: var(--fg-dim); }
.cx-note       { --kind: var(--fg-faint); }
.cx-recap      { --kind: var(--ok); }
.cx-hint       { --kind: var(--warn); }
.cx-solution   { --kind: var(--fg-faint); }
.cx-interview  { --kind: var(--accent-2); }
.cx-try        { --kind: var(--ok); background: color-mix(in srgb, var(--ok) 4%, var(--bg-2)); }
.cx-connect    { --kind: var(--info); background: color-mix(in srgb, var(--info) 6%, var(--bg-2)); }
.cx-analogy    { --kind: var(--warn); background: color-mix(in srgb, var(--warn) 5%, var(--bg-2)); }
.cx-resources  { --kind: var(--fg-dim); }

.cx-stop {
  --kind: var(--danger); border: 1px solid var(--danger);
  background: color-mix(in srgb, var(--danger) 10%, var(--bg-2));
}
.cx-stop .cx-kind { font-size: 13px; letter-spacing: .14em; }

details.cx > summary {
  display: flex; align-items: baseline; gap: 10px; padding: 14px 20px; cursor: pointer; list-style: none;
}
details.cx > summary::-webkit-details-marker { display: none; }
details.cx > summary:hover { background: var(--bg-3); }
details.cx[open] > summary { border-bottom: 1px solid var(--line); }
.cx-toggle { margin-left: auto; font-size: 11px; color: var(--fg-faint); font-family: var(--mono); }

/* task lists inside blocks */
.cx-body ul:has(input[type="checkbox"]), .prose ul:has(input[type="checkbox"]) { list-style: none; padding-left: 2px; }
.prose li:has(input[type="checkbox"]) { display: flex; gap: 9px; align-items: flex-start; }
.prose li input[type="checkbox"] { margin-top: 6px; accent-color: var(--ok); width: 15px; height: 15px; flex: none; cursor: pointer; }
.prose li.checked { color: var(--fg-faint); text-decoration: line-through; text-decoration-color: var(--fg-faint); }

/* ---------- lesson chrome ---------- */
.lesson-head { padding-bottom: 6px; }
.crumb { font-size: 14px; color: var(--fg-faint); margin: 0 0 8px; }
.lesson-meta { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 14px; }
.chip {
  font-size: 12.5px; font-weight: 600; padding: 3px 9px; border-radius: 99px;
  background: var(--bg-3); color: var(--fg-dim); border: 1px solid var(--line);
}
.chip-exercise { color: var(--ok); border-color: color-mix(in srgb, var(--ok) 40%, var(--line)); }
.chip-challenge { color: var(--accent-2); border-color: color-mix(in srgb, var(--accent-2) 40%, var(--line)); }
.chip-project { color: var(--accent); border-color: color-mix(in srgb, var(--accent) 40%, var(--line)); }
.chip-debug { color: var(--danger); }
.chip-stage { color: var(--warn); border-color: color-mix(in srgb, var(--warn) 40%, var(--line)); }

.lesson-foot { margin-top: 48px; border-top: 1px solid var(--line); padding-top: 24px; }
.btn {
  display: inline-block; padding: 9px 17px; border-radius: var(--radius-s); border: 1px solid var(--line);
  background: var(--bg-2); color: var(--fg); font-size: 14px; font-weight: 600; cursor: pointer; font-family: inherit;
}
.btn:hover { border-color: var(--accent); text-decoration: none; }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn.primary:hover { filter: brightness(1.08); }
.complete-btn.is-done { background: var(--ok); border-color: var(--ok); }
.pager { display: flex; gap: 12px; margin-top: 24px; }
.pg {
  flex: 1; display: flex; flex-direction: column; gap: 2px; padding: 12px 15px;
  border: 1px solid var(--line); border-radius: var(--radius); background: var(--bg-2);
}
.pg:hover { border-color: var(--accent); text-decoration: none; }
.pg span { font-size: 11px; text-transform: uppercase; letter-spacing: .08em; color: var(--fg-faint); }
.pg strong { font-size: 16px; color: var(--fg); font-weight: 600; }
.pg.next { text-align: right; }

/* ---------- roadmap & project ---------- */
.roadmap, .stages { list-style: none; padding: 0; }
.roadmap > li { border-left: 2px solid var(--line); padding: 0 0 26px 22px; position: relative; }
.roadmap > li::before {
  content: ""; position: absolute; left: -6px; top: 8px; width: 10px; height: 10px;
  border-radius: 50%; background: var(--bg); border: 2px solid var(--line);
}
.roadmap > li.started::before { border-color: var(--accent); }
.roadmap > li.complete::before { background: var(--ok); border-color: var(--ok); }
.rm-head { display: flex; align-items: baseline; gap: 10px; }
.rm-head h2 { margin: 0; font-size: 18px; }
.rm-num { font-family: var(--mono); font-size: 11px; color: var(--fg-faint); }
.rm-count { margin-left: auto; font-family: var(--mono); font-size: 11.5px; color: var(--fg-faint); }
.rm-goal { font-size: 13.5px; color: var(--fg-dim); margin: 6px 0 10px; }
.rm-lessons { list-style: none; padding: 0; margin: 0; }
.rm-lessons a { display: flex; gap: 9px; align-items: baseline; padding: 4px 8px; border-radius: 6px; font-size: 14px; color: var(--fg-dim); }
.rm-lessons a:hover { background: var(--bg-3); text-decoration: none; color: var(--fg); }
.rm-lessons a.done { color: var(--fg-faint); }
.rm-lessons em { margin-left: auto; font-style: normal; font-size: 11.5px; color: var(--fg-faint); font-family: var(--mono); }
.callout-plain { background: var(--bg-2); border: 1px solid var(--line); border-radius: var(--radius); padding: 13px 16px; font-size: 14px; margin: 18px 0 26px; }
.stages > li { display: flex; gap: 14px; padding: 16px 0; border-bottom: 1px solid var(--line); }
.stages > li.complete h2 { color: var(--ok); }
.stage-check input { width: 18px; height: 18px; accent-color: var(--ok); cursor: pointer; margin-top: 5px; }
.stage-head { display: flex; align-items: baseline; gap: 10px; flex-wrap: wrap; }
.stage-head h2 { margin: 0; font-size: 17px; }
.stage-phase { font-size: 11px; color: var(--fg-faint); font-family: var(--mono); }
.stages p { margin: 6px 0; font-size: 14px; color: var(--fg-dim); }
.stage-list { margin: 8px 0; font-size: 13.5px; color: var(--fg-dim); }
.stage-run code { font-size: 12px; }

/* ---------- search ---------- */
.search-modal { position: fixed; inset: 0; z-index: 90; background: rgba(0,0,0,.5); backdrop-filter: blur(3px); padding-top: 9vh; }
.search-panel {
  max-width: 620px; margin: 0 auto; background: var(--bg-2); border: 1px solid var(--line);
  border-radius: var(--radius); box-shadow: var(--shadow); overflow: hidden;
}
#search-input {
  width: 100%; border: 0; border-bottom: 1px solid var(--line); background: none; color: var(--fg);
  font-size: 16px; padding: 15px 18px; font-family: inherit; outline: none;
}
.search-results { max-height: 52vh; overflow-y: auto; }
.sr { display: block; padding: 10px 18px; border-bottom: 1px solid var(--line); color: var(--fg); }
.sr:hover, .sr.sel { background: var(--accent-soft); text-decoration: none; }
.sr-phase { font-size: 10.5px; text-transform: uppercase; letter-spacing: .07em; color: var(--fg-faint); }
.sr strong { display: block; font-size: 14.5px; margin: 1px 0 2px; }
.sr-snip { font-size: 12.5px; color: var(--fg-dim); display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden; }
.sr-empty { padding: 20px 18px; color: var(--fg-faint); font-size: 14px; }
.search-foot { padding: 8px 18px; font-size: 11.5px; color: var(--fg-faint); border-top: 1px solid var(--line); }
.loading { color: var(--fg-faint); }

/* ---------- lesson layout: column + outline rail ---------- */
.lesson-layout {
  display: grid; grid-template-columns: minmax(0, var(--lesson-w)) var(--rail-w);
  gap: 56px; justify-content: center; padding: 40px 40px 120px;
}
.lesson { min-width: 0; }
.rail { position: sticky; top: calc(var(--topbar-h) + 24px); align-self: start; max-height: calc(100vh - var(--topbar-h) - 40px); overflow-y: auto; }
.rail-inner { display: flex; flex-direction: column; gap: 16px; padding-bottom: 20px; }
.rail-label { font-size: 12px; text-transform: uppercase; letter-spacing: .09em; color: var(--fg-faint); font-weight: 700; margin: 4px 0 -8px; }
.mode-switch { display: grid; grid-template-columns: 1fr 1fr; background: var(--bg-3); border: 1px solid var(--line); border-radius: 10px; padding: 3px; }
.mode-switch button {
  background: none; border: 0; border-radius: 7px; padding: 7px 6px; font: inherit; font-size: 12.5px; font-weight: 600;
  color: var(--fg-dim); cursor: pointer; line-height: 1.25;
}
.mode-switch button[aria-pressed="true"] { background: var(--bg-2); color: var(--fg); box-shadow: 0 1px 3px rgba(0,0,0,.18); }
.rail-steps { list-style: none; margin: 0; padding: 0; position: relative; }
.rail-steps li a {
  display: flex; align-items: flex-start; gap: 10px; padding: 7px 8px; border-radius: 8px;
  font-size: 14px; line-height: 1.35; color: var(--fg-dim);
}
.rail-steps li a:hover { background: var(--bg-3); color: var(--fg); text-decoration: none; }
.rs-dot {
  flex: none; display: grid; place-items: center; width: 22px; height: 22px; border-radius: 50%;
  border: 1.5px solid var(--line); font-size: 11px; font-weight: 700; color: var(--fg-faint); font-family: var(--mono);
}
.rs-title { flex: 1; padding-top: 1px; }
.rs-q { flex: none; font-size: 11px; font-weight: 700; color: var(--accent-2); padding-top: 3px; font-family: var(--mono); }
.rs-seen .rs-dot { border-color: var(--fg-faint); color: var(--fg-dim); }
.rs-passed .rs-dot { background: var(--ok); border-color: var(--ok); color: #fff; }
.rs-revealed .rs-dot { border-color: var(--warn); color: var(--warn); }
.rail-steps li.current a { background: var(--accent-soft); color: var(--fg); font-weight: 600; }
.rail-steps li.current .rs-dot { border-color: var(--accent); color: var(--accent); }
.rail-steps li.current.rs-passed .rs-dot { color: #fff; }
.rail-card { background: var(--bg-2); border: 1px solid var(--line); border-radius: var(--radius); padding: 13px 15px; font-size: 13.5px; }
.rail-card p { margin: 8px 0 0; color: var(--fg-dim); line-height: 1.5; }
.rc-row { display: flex; justify-content: space-between; margin-bottom: 8px; color: var(--fg-dim); }
.rc-row strong { color: var(--fg); }
.rail-tip strong { font-size: 12px; text-transform: uppercase; letter-spacing: .08em; color: var(--fg-faint); }

/* ---------- stepper (one step at a time) ---------- */
.stepper {
  position: sticky; top: var(--topbar-h); z-index: 20; margin: 22px -12px 6px; padding: 12px 12px 12px;
  background: color-mix(in srgb, var(--bg) 92%, transparent); backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line); scroll-margin-top: var(--topbar-h);
}
.stepper-row { display: flex; align-items: baseline; gap: 12px; margin-bottom: 9px; }
.stepper-count { font-size: 12px; font-weight: 700; text-transform: uppercase; letter-spacing: .08em; color: var(--accent); white-space: nowrap; }
.stepper-title { font-size: 14.5px; color: var(--fg-dim); white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.segments { display: flex; gap: 4px; }
.segments { margin: -6px 0; }
.seg { flex: 1; height: 18px; border: 0; padding: 0; background: none; cursor: pointer; position: relative; }
.seg::before { content: ""; position: absolute; left: 0; right: 0; top: 6px; height: 6px; border-radius: 99px; background: var(--bg-3); transition: background .2s; }
.seg:hover::before { background: var(--line); }
.seg.before::before, .seg.seg-seen::before { background: color-mix(in srgb, var(--accent) 45%, var(--bg-3)); }
.seg.seg-passed::before { background: var(--ok); }
.seg.seg-revealed::before { background: var(--warn); }
.seg.current::before { background: var(--accent); box-shadow: 0 0 0 2px color-mix(in srgb, var(--accent) 30%, transparent); }
.step[hidden] { display: none; }
.step > h2:first-child { margin-top: 26px; }
body.mode-full .step + .step { border-top: 1px dashed var(--line); margin-top: 36px; }

.step-nav {
  display: grid; grid-template-columns: auto 1fr auto; align-items: center; gap: 16px;
  margin-top: 40px; padding-top: 22px; border-top: 1px solid var(--line);
}
.sn-note { font-size: 14px; color: var(--fg-faint); text-align: center; }
.sn-next { display: flex; flex-direction: column; align-items: flex-end; gap: 1px; padding: 11px 20px; max-width: 360px; text-align: right; }
.sn-next span { font-size: 11.5px; text-transform: uppercase; letter-spacing: .08em; opacity: .8; font-weight: 700; }
.sn-next strong { font-size: 15.5px; line-height: 1.3; }
.sn-prev { padding: 11px 18px; }
.lesson-foot[hidden] { display: none; }
.finish { display: flex; gap: 12px; align-items: center; flex-wrap: wrap; }

/* ---------- knowledge check ---------- */
.cx-quiz { --kind: var(--accent-2); background: color-mix(in srgb, var(--accent-2) 6%, var(--bg-2)); border-left-width: 4px; }
.quiz-q > :first-child { margin-top: 8px; }
.quiz-q p { font-weight: 550; }
.quiz-opts { display: grid; gap: 8px; margin: 14px 0 4px; }
.quiz-opt {
  display: flex; align-items: flex-start; gap: 12px; width: 100%; text-align: left;
  padding: 11px 14px; border: 1.5px solid var(--line); border-radius: 10px; background: var(--bg-2);
  color: var(--fg); font: inherit; font-size: 16px; line-height: 1.5; cursor: pointer; transition: border-color .15s, background .15s;
}
.quiz-opt:hover:not(:disabled) { border-color: color-mix(in srgb, var(--accent-2) 60%, var(--line)); }
.quiz-opt[aria-checked="true"] { border-color: var(--accent-2); background: color-mix(in srgb, var(--accent-2) 10%, var(--bg-2)); }
.quiz-opt:disabled { cursor: default; }
.quiz-letter {
  flex: none; display: grid; place-items: center; width: 24px; height: 24px; margin-top: 1px; border-radius: 6px;
  background: var(--bg-3); font-size: 12px; font-weight: 750; color: var(--fg-dim); font-family: var(--mono);
}
.quiz-opt[aria-checked="true"] .quiz-letter { background: var(--accent-2); color: #fff; }
.quiz-opt.is-wrong { border-color: color-mix(in srgb, var(--danger) 55%, var(--line)); opacity: .7; }
.quiz-opt.is-wrong .quiz-text { text-decoration: line-through; text-decoration-color: var(--danger); }
.quiz-opt.is-wrong .quiz-letter { background: var(--danger); color: #fff; }
.quiz-opt.is-right { border-color: var(--ok); background: color-mix(in srgb, var(--ok) 10%, var(--bg-2)); opacity: 1; }
.quiz-opt.is-right .quiz-letter { background: var(--ok); color: #fff; }
.is-finished .quiz-opt:not(.is-right):not(.is-wrong) { opacity: .55; }
.quiz-bar { display: flex; align-items: center; gap: 14px; flex-wrap: wrap; margin-top: 14px; }
.quiz-check[hidden], .quiz-reveal[hidden] { display: none; }
.quiz-check:disabled { opacity: .45; cursor: not-allowed; filter: none; }
.quiz-feedback { font-size: 15px; font-weight: 600; }
.quiz-feedback.good { color: var(--ok); }
.quiz-feedback.bad { color: var(--danger); }
.quiz-feedback.meh { color: var(--warn); }
.linkish { background: none; border: 0; padding: 0; font: inherit; font-size: 14.5px; color: var(--accent); cursor: pointer; text-decoration: underline; text-underline-offset: 3px; }
.quiz-explain { margin-top: 14px; padding: 12px 16px; border-radius: 10px; background: var(--bg-3); }
.quiz-explain > :first-child { margin-top: 0; }
.quiz-explain > :last-child { margin-bottom: 0; }
.quiz-explain::before { content: "Why"; display: block; font-size: 11.5px; font-weight: 750; letter-spacing: .09em; text-transform: uppercase; color: var(--fg-faint); margin-bottom: 4px; }
.chip-quiz { color: var(--accent-2); border-color: color-mix(in srgb, var(--accent-2) 40%, var(--line)); }

/* ---------- home ---------- */
.hero { display: grid; grid-template-columns: minmax(0, 1.25fr) minmax(300px, .9fr); gap: 40px; align-items: center; padding: 20px 0 8px; }
.hero h1 { font-size: 44px; max-width: 16ch; }
.hero .lede { max-width: 52ch; }
.next-card {
  display: flex; flex-direction: column; gap: 4px; padding: 24px 26px; border-radius: 18px; color: var(--fg);
  background: linear-gradient(160deg, color-mix(in srgb, var(--accent) 16%, var(--bg-2)), var(--bg-2) 70%);
  border: 1px solid color-mix(in srgb, var(--accent) 35%, var(--line)); box-shadow: var(--shadow);
  transition: transform .15s, border-color .15s;
}
.next-card:hover { text-decoration: none; transform: translateY(-2px); border-color: var(--accent); }
.nc-label { font-size: 12px; text-transform: uppercase; letter-spacing: .1em; font-weight: 750; color: var(--accent); }
.nc-phase { font-size: 14px; color: var(--fg-dim); margin-top: 8px; }
.nc-title { font-size: 24px; line-height: 1.25; letter-spacing: -.01em; }
.nc-meta { font-size: 14px; color: var(--fg-faint); }
.nc-go {
  align-self: flex-start; margin-top: 14px; padding: 10px 20px; border-radius: 10px; background: var(--accent);
  color: #fff; font-weight: 700; font-size: 15.5px;
}
.nc-progress { display: flex; align-items: center; gap: 12px; margin-top: 18px; font-size: 13px; color: var(--fg-faint); }
.nc-progress .bar { flex: 1; }
.how { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 14px; margin: 44px 0 10px; }
.how-step { padding: 16px 18px; border-radius: var(--radius); background: var(--bg-2); border: 1px solid var(--line); }
.how-num {
  display: grid; place-items: center; width: 26px; height: 26px; border-radius: 50%;
  background: var(--accent-soft); color: var(--accent); font-size: 13px; font-weight: 750; margin-bottom: 10px;
}
.how-step strong { display: block; font-size: 16px; }
.how-step p { margin: 4px 0 0; font-size: 14.5px; color: var(--fg-dim); line-height: 1.5; }
.section-head { display: flex; align-items: baseline; justify-content: space-between; gap: 16px; flex-wrap: wrap; margin: 40px 0 14px; }
.section-head h2 { margin: 0; }
.section-head span { font-size: 14px; color: var(--fg-faint); }
.phase-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); gap: 14px; }
.phase-card {
  display: block; padding: 18px 20px; border: 1px solid var(--line); border-radius: var(--radius);
  background: var(--bg-2); color: var(--fg); transition: transform .15s, border-color .15s;
}
.phase-card:hover { border-color: var(--accent); text-decoration: none; transform: translateY(-1px); }
.phase-card.current { border-color: color-mix(in srgb, var(--accent) 55%, var(--line)); box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--accent) 30%, transparent); }
.phase-card.current .pc-num { color: var(--accent); }
.phase-card.complete .pc-num { color: var(--ok); }
.pc-num { font-family: var(--mono); font-size: 12px; color: var(--fg-faint); letter-spacing: .04em; }
.phase-card h3 { margin: 6px 0 6px; font-size: 18px; }
.phase-card p { font-size: 14.5px; color: var(--fg-dim); margin: 0 0 14px; line-height: 1.5; }
.pc-meta { font-size: 12.5px; color: var(--fg-faint); display: block; margin-top: 8px; }

/* ---------- responsive ---------- */
@media (max-width: 1280px) {
  .lesson-layout { grid-template-columns: minmax(0, var(--lesson-w)); padding: 36px 36px 110px; }
  .rail { display: none; }
}
@media (max-width: 1100px) {
  .hero { grid-template-columns: 1fr; }
  .how { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}
@media (max-width: 960px) {
  #menu-btn { display: block; }
  .brand-text { display: none; }
  .sidebar {
    position: fixed; top: var(--topbar-h); left: 0; z-index: 50;
    transform: translateX(-100%); transition: transform .2s ease; box-shadow: var(--shadow);
  }
  .sidebar.open { transform: none; }
  .scrim { display: block; position: fixed; inset: var(--topbar-h) 0 0; background: rgba(0,0,0,.45); opacity: 0; pointer-events: none; transition: opacity .2s; z-index: 45; }
  .scrim.show { opacity: 1; pointer-events: auto; }
  .page, .lesson-layout { padding: 24px 16px 90px; }
  .hero h1 { font-size: 32px; }
  h1 { font-size: 30px; }
  h2 { font-size: 23px; }
  body { font-size: 16.5px; }
  pre code { font-size: 14px; }
  .how { grid-template-columns: 1fr; }
  .stepper { margin-left: -16px; margin-right: -16px; padding-left: 16px; padding-right: 16px; }
  .step-nav { grid-template-columns: auto 1fr; }
  .sn-note { grid-column: 1 / -1; order: -1; }
  .sn-next { justify-self: end; }
  .topbar-right .ghost-btn { display: none; }
  .pager { flex-direction: column; }
  .pg.next { text-align: left; }
}
@media (prefers-reduced-motion: reduce) { * { transition: none !important; scroll-behavior: auto; } }