/* ==========================================================================
   Learn Robinhood Chain — design system
   Dark-first, theme-aware, one accent gradient. No CDN, system font stack.
   ========================================================================== */

:root,
:root[data-theme='dark'] {
  color-scheme: dark;
  --bg: #0b0d10;
  --bg-elev: #111418;
  --bg-elev-2: #171b21;
  --bg-code: #0e1116;
  --border: #232a33;
  --border-strong: #2f3946;
  --fg: #e7ecf2;
  --fg-muted: #9aa7b6;
  --fg-faint: #66727f;
  --accent: #00c805;
  --accent-2: #34e27a;
  --accent-ink: #04120a;
  --accent-soft: rgba(0, 200, 5, 0.12);
  --accent-line: rgba(0, 200, 5, 0.35);
  --danger: #ff5c5c;
  --warn: #ffb020;
  --info: #4aa8ff;
  --grad: linear-gradient(100deg, #00c805 0%, #34e27a 55%, #7bf5a8 100%);
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 8px 30px rgba(0, 0, 0, 0.35);

  /* code highlighting */
  --code-fg: #d6dee8;
  --hl-comment: #6b7789;
  --hl-keyword: #ff7ab2;
  --hl-string: #79e07a;
  --hl-number: #f2c66d;
  --hl-title: #6cb6ff;
  --hl-type: #7ee0c8;
  --hl-var: #d6dee8;
  --hl-attr: #b48ef0;
  --hl-deletion: #ff8b8b;

  --radius: 12px;
  --radius-sm: 8px;
  --maxw: 1320px;
  --sidebar-w: 288px;
  --toc-w: 220px;
  --font: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  --mono: ui-monospace, 'SF Mono', 'SFMono-Regular', Menlo, Monaco, Consolas, 'Liberation Mono', monospace;
}

:root[data-theme='light'] {
  color-scheme: light;
  --bg: #ffffff;
  --bg-elev: #f7f9fb;
  --bg-elev-2: #eef2f6;
  --bg-code: #f6f8fa;
  --border: #e3e8ee;
  --border-strong: #d2dae3;
  --fg: #0f1720;
  --fg-muted: #52606d;
  --fg-faint: #7b8794;
  --accent: #008a04;
  --accent-2: #00a838;
  --accent-ink: #ffffff;
  --accent-soft: rgba(0, 138, 4, 0.1);
  --accent-line: rgba(0, 138, 4, 0.3);
  --grad: linear-gradient(100deg, #008a04 0%, #00a838 60%, #22b455 100%);
  --shadow: 0 1px 2px rgba(16, 23, 32, 0.06), 0 10px 30px rgba(16, 23, 32, 0.08);

  --code-fg: #24292f;
  --hl-comment: #6e7781;
  --hl-keyword: #cf222e;
  --hl-string: #0a7d33;
  --hl-number: #953800;
  --hl-title: #0550ae;
  --hl-type: #1b7c83;
  --hl-var: #24292f;
  --hl-attr: #6639ba;
  --hl-deletion: #82071e;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 84px; }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } * { animation-duration: 0.001ms !important; transition-duration: 0.001ms !important; } }

body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--fg);
  font-size: 16px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

a { color: var(--accent-2); text-decoration: none; }
a:hover { text-decoration: underline; }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 4px; }

.skip-link {
  position: absolute; left: -999px; top: 8px; z-index: 200;
  background: var(--accent); color: var(--accent-ink); padding: 8px 14px; border-radius: 8px; font-weight: 600;
}
.skip-link:focus { left: 12px; }

kbd {
  font-family: var(--mono); font-size: 11px; line-height: 1;
  padding: 3px 6px; border: 1px solid var(--border-strong); border-bottom-width: 2px;
  border-radius: 6px; background: var(--bg-elev-2); color: var(--fg-muted);
}

/* ---------- topbar -------------------------------------------------------- */
.topbar {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: saturate(160%) blur(12px);
  border-bottom: 1px solid var(--border);
}
.topbar-inner {
  max-width: var(--maxw); margin: 0 auto; height: 60px;
  display: flex; align-items: center; justify-content: space-between; gap: 16px;
  padding: 0 20px;
}
.brand { display: flex; align-items: center; gap: 10px; color: var(--fg); font-size: 15px; }
.brand:hover { text-decoration: none; }
.brand-mark {
  width: 28px; height: 28px; border-radius: 7px; display: grid; place-items: center;
  background: var(--grad); color: #04120a; font-weight: 800; font-size: 16px; flex: none;
}
.brand-text strong { font-weight: 700; }
.brand-text { color: var(--fg-muted); font-weight: 500; }
.brand-text strong { color: var(--fg); }

.topbar-actions { display: flex; align-items: center; gap: 8px; }
.ghost-link { color: var(--fg-muted); font-size: 14px; padding: 6px 8px; border-radius: 8px; }
.ghost-link:hover { color: var(--fg); text-decoration: none; background: var(--bg-elev-2); }

.search-open {
  display: inline-flex; align-items: center; gap: 10px;
  background: var(--bg-elev-2); border: 1px solid var(--border); color: var(--fg-muted);
  padding: 7px 10px; border-radius: 9px; font-size: 13px; cursor: pointer; min-width: 160px;
  justify-content: space-between; font-family: inherit;
}
.search-open:hover { border-color: var(--border-strong); color: var(--fg); }
.search-open kbd { padding: 2px 6px; }

.theme-toggle, .menu-toggle {
  width: 36px; height: 36px; border-radius: 9px; border: 1px solid var(--border);
  background: var(--bg-elev-2); cursor: pointer; display: grid; place-items: center; color: var(--fg-muted);
}
.theme-toggle:hover, .menu-toggle:hover { color: var(--fg); border-color: var(--border-strong); }
.theme-toggle::before { content: '☾'; font-size: 16px; }
:root[data-theme='light'] .theme-toggle::before { content: '☀'; }
.menu-toggle { display: none; }
.menu-toggle::before { content: '≡'; font-size: 20px; }

/* ---------- layout -------------------------------------------------------- */
.layout { max-width: var(--maxw); margin: 0 auto; display: flex; align-items: flex-start; }

.sidebar {
  position: sticky; top: 60px; align-self: flex-start;
  width: var(--sidebar-w); flex: none; height: calc(100vh - 60px);
  overflow-y: auto; padding: 24px 12px 60px 20px; border-right: 1px solid var(--border);
}
.nav-section { margin-bottom: 22px; }
.nav-section-title {
  font-size: 11px; text-transform: uppercase; letter-spacing: 0.09em; color: var(--fg-faint);
  font-weight: 700; margin: 0 0 8px 10px;
}
.sidebar-nav ul { list-style: none; margin: 0; padding: 0; }
.sidebar-nav li a {
  display: flex; align-items: center; gap: 10px; padding: 7px 10px; border-radius: 8px;
  color: var(--fg-muted); font-size: 14px; line-height: 1.35;
}
.sidebar-nav li a:hover { background: var(--bg-elev-2); color: var(--fg); text-decoration: none; }
.sidebar-nav li a.active { background: var(--accent-soft); color: var(--fg); font-weight: 600; }
.sidebar-nav li a.active .nav-idx { color: var(--accent-2); border-color: var(--accent-line); }
.nav-idx {
  flex: none; width: 24px; height: 20px; display: grid; place-items: center;
  font-family: var(--mono); font-size: 11px; color: var(--fg-faint);
  border: 1px solid var(--border); border-radius: 6px;
}
.sidebar-nav li a.done .nav-idx::after { content: ''; }

.sidebar-scrim { display: none; }

/* ---------- landing ------------------------------------------------------- */
.landing { flex: 1; min-width: 0; padding: 0 20px; }
.hero { padding: 72px 0 40px; border-bottom: 1px solid var(--border); }
.hero-inner { max-width: 820px; }
.eyebrow {
  font-family: var(--mono); font-size: 12.5px; color: var(--fg-muted); margin: 0 0 18px;
  letter-spacing: 0.01em;
}
.hero h1 { font-size: clamp(38px, 6vw, 62px); line-height: 1.03; letter-spacing: -0.03em; margin: 0 0 20px; font-weight: 800; }
.grad { background: var(--grad); -webkit-background-clip: text; background-clip: text; color: transparent; }
.lede { font-size: clamp(17px, 2.2vw, 20px); color: var(--fg-muted); margin: 0 0 28px; max-width: 680px; }
.hero-cta { display: flex; gap: 12px; flex-wrap: wrap; margin-bottom: 40px; }
.btn {
  display: inline-flex; align-items: center; gap: 8px; padding: 12px 20px; border-radius: 10px;
  font-weight: 600; font-size: 15px; cursor: pointer; border: 1px solid transparent; transition: transform 0.06s ease, background 0.15s ease, border-color 0.15s ease;
}
.btn:hover { text-decoration: none; }
.btn:active { transform: translateY(1px); }
.btn-primary { background: var(--accent); color: var(--accent-ink); }
.btn-primary:hover { background: var(--accent-2); }
.btn-ghost { background: var(--bg-elev); border-color: var(--border-strong); color: var(--fg); }
.btn-ghost:hover { background: var(--bg-elev-2); border-color: var(--fg-faint); }

.chain-strip {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 1px;
  background: var(--border); border: 1px solid var(--border); border-radius: var(--radius); overflow: hidden;
}
.stat { background: var(--bg-elev); padding: 16px 18px; display: flex; flex-direction: column; gap: 6px; }
.stat-label { font-size: 12px; color: var(--fg-faint); text-transform: uppercase; letter-spacing: 0.06em; font-weight: 600; }
.stat-value { font-family: var(--mono); font-size: 19px; font-weight: 600; font-variant-numeric: tabular-nums; }
.stat-value.tick { animation: flash 0.6s ease; }
@keyframes flash { 0% { color: var(--accent-2); } 100% { color: var(--fg); } }
.chain-strip-note { font-size: 12.5px; color: var(--fg-faint); margin: 10px 2px 0; }
.chain-strip-note.err { color: var(--warn); }

.curriculum { padding: 48px 0 24px; }
.curriculum-head { display: flex; align-items: baseline; justify-content: space-between; gap: 12px; }
.section-h { font-size: 26px; letter-spacing: -0.02em; margin: 0; font-weight: 700; }
.reset-progress { background: none; border: 1px solid var(--border); color: var(--fg-muted); font-size: 12.5px; padding: 5px 10px; border-radius: 7px; cursor: pointer; font-family: inherit; }
.reset-progress:hover { color: var(--fg); border-color: var(--border-strong); }
.progress-line { color: var(--fg-muted); font-size: 14px; margin: 8px 0 32px; }
#progress-count { color: var(--accent-2); font-weight: 700; }

.curriculum-group { margin-bottom: 40px; }
.curriculum-group-title {
  font-size: 13px; text-transform: uppercase; letter-spacing: 0.1em; color: var(--fg-faint);
  font-weight: 700; margin: 0 0 16px; padding-bottom: 10px; border-bottom: 1px solid var(--border);
}
.card-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 14px; }
.tut-card {
  position: relative; display: flex; gap: 14px; padding: 18px; border: 1px solid var(--border);
  border-radius: var(--radius); background: var(--bg-elev); color: var(--fg); overflow: hidden;
  transition: border-color 0.15s ease, transform 0.08s ease, background 0.15s ease;
}
.tut-card::before { content: ''; position: absolute; inset: 0 auto 0 0; width: 3px; background: var(--grad); opacity: 0; transition: opacity 0.15s ease; }
.tut-card:hover { text-decoration: none; border-color: var(--border-strong); transform: translateY(-2px); background: var(--bg-elev-2); }
.tut-card:hover::before { opacity: 1; }
.tut-card-idx { font-family: var(--mono); font-size: 13px; color: var(--fg-faint); flex: none; padding-top: 1px; }
.tut-card-body { display: flex; flex-direction: column; gap: 5px; min-width: 0; }
.tut-card-title { font-weight: 650; font-size: 15.5px; letter-spacing: -0.01em; }
.tut-card-desc { color: var(--fg-muted); font-size: 13.5px; line-height: 1.5; }
.tut-card-time { color: var(--fg-faint); font-size: 12px; font-family: var(--mono); margin-top: 2px; }
.tut-card-check {
  position: absolute; top: 14px; right: 14px; width: 18px; height: 18px; border-radius: 50%;
  border: 1.5px solid var(--border-strong); flex: none; transition: all 0.15s ease;
}
.tut-card.done { border-color: var(--accent-line); }
.tut-card.done .tut-card-check { background: var(--accent); border-color: var(--accent); }
.tut-card.done .tut-card-check::after { content: '✓'; color: var(--accent-ink); font-size: 12px; font-weight: 800; display: grid; place-items: center; height: 100%; }
.tut-card.done .tut-card-idx { color: var(--accent-2); }

.site-footer { border-top: 1px solid var(--border); padding: 32px 0 60px; color: var(--fg-muted); font-size: 14px; }
.site-footer p { margin: 0 0 8px; }
.disclaimer { color: var(--fg-faint); font-size: 12.5px; max-width: 720px; line-height: 1.6; }

/* ---------- doc page ------------------------------------------------------ */
.doc { flex: 1; min-width: 0; display: flex; gap: 32px; padding: 32px 20px 80px; }
.doc-article { flex: 1; min-width: 0; max-width: 760px; }
.breadcrumb { display: flex; gap: 8px; align-items: center; font-size: 13px; color: var(--fg-faint); margin-bottom: 18px; }
.breadcrumb a { color: var(--fg-muted); }
.doc-header h1 { font-size: clamp(30px, 4.5vw, 40px); line-height: 1.1; letter-spacing: -0.025em; margin: 0 0 14px; font-weight: 800; }
.doc-meta { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; color: var(--fg-muted); font-size: 13.5px; margin-bottom: 28px; }
.doc-meta-item { font-family: var(--mono); }
.doc-meta-sep { color: var(--fg-faint); }
.done-toggle { display: inline-flex; align-items: center; gap: 7px; cursor: pointer; font-family: var(--font); }
.done-toggle input { accent-color: var(--accent); width: 15px; height: 15px; }

.whatbuild, .prereq {
  border: 1px solid var(--border); border-radius: var(--radius); padding: 16px 18px; margin: 0 0 18px;
  background: var(--bg-elev);
}
.whatbuild { border-left: 3px solid var(--accent); }
.whatbuild-title, .prereq-title { font-weight: 700; font-size: 13px; text-transform: uppercase; letter-spacing: 0.06em; margin: 0 0 8px; color: var(--fg-muted); }
.whatbuild p:last-child { margin: 0; }
.prereq ul { margin: 0; padding-left: 20px; }
.prereq li { margin: 4px 0; color: var(--fg-muted); font-size: 14.5px; }
.prereq li code { color: var(--fg); }

/* body typography */
.doc-body { font-size: 16px; }
.doc-body > *:first-child { margin-top: 0; }
.doc-body h2 { font-size: 25px; letter-spacing: -0.02em; margin: 48px 0 16px; padding-top: 8px; font-weight: 700; }
.doc-body h3 { font-size: 19px; letter-spacing: -0.01em; margin: 32px 0 12px; font-weight: 650; }
.doc-body h2 .anchor, .doc-body h3 .anchor {
  opacity: 0; margin-left: -22px; padding-right: 8px; color: var(--fg-faint); font-weight: 400; text-decoration: none;
}
.doc-body h2:hover .anchor, .doc-body h3:hover .anchor { opacity: 1; }
.doc-body p { margin: 0 0 16px; }
.doc-body ul, .doc-body ol { margin: 0 0 16px; padding-left: 24px; }
.doc-body li { margin: 6px 0; }
.doc-body li::marker { color: var(--fg-faint); }
.doc-body strong { color: var(--fg); font-weight: 650; }
.doc-body hr { border: none; border-top: 1px solid var(--border); margin: 40px 0; }

.doc-body :not(pre) > code {
  font-family: var(--mono); font-size: 0.86em; padding: 2px 6px; border-radius: 6px;
  background: var(--bg-elev-2); border: 1px solid var(--border); color: var(--fg);
  word-break: break-word;
}

.doc-body blockquote {
  margin: 0 0 16px; padding: 2px 18px; border-left: 3px solid var(--border-strong);
  color: var(--fg-muted);
}

.doc-body table { width: 100%; border-collapse: collapse; margin: 0 0 20px; font-size: 14.5px; display: block; overflow-x: auto; }
.doc-body thead { background: var(--bg-elev); }
.doc-body th, .doc-body td { border: 1px solid var(--border); padding: 9px 13px; text-align: left; vertical-align: top; }
.doc-body th { font-weight: 650; color: var(--fg); }
.doc-body td code { white-space: nowrap; }

.doc-body img { max-width: 100%; height: auto; border-radius: var(--radius); border: 1px solid var(--border); }

/* code blocks */
.code-block { margin: 0 0 20px; border: 1px solid var(--border); border-radius: var(--radius); overflow: hidden; background: var(--bg-code); }
.code-block figcaption {
  display: flex; align-items: center; justify-content: space-between;
  padding: 7px 12px 7px 14px; border-bottom: 1px solid var(--border); background: var(--bg-elev);
}
.code-lang { font-family: var(--mono); font-size: 11.5px; color: var(--fg-faint); text-transform: none; letter-spacing: 0.02em; }
.copy-btn {
  font-family: var(--font); font-size: 12px; color: var(--fg-muted); background: var(--bg-elev-2);
  border: 1px solid var(--border); padding: 4px 10px; border-radius: 7px; cursor: pointer;
}
.copy-btn:hover { color: var(--fg); border-color: var(--border-strong); }
.copy-btn.copied { color: var(--accent-2); border-color: var(--accent-line); }
.code-block pre { margin: 0; padding: 16px; overflow-x: auto; }
.code-block code { font-family: var(--mono); font-size: 13.5px; line-height: 1.6; }

/* callouts */
.callout { border: 1px solid var(--border); border-left-width: 3px; border-radius: var(--radius); padding: 14px 18px; margin: 0 0 20px; background: var(--bg-elev); }
.callout p:last-child { margin-bottom: 0; }
.callout-title { font-weight: 700; font-size: 13px; text-transform: uppercase; letter-spacing: 0.05em; margin: 0 0 6px; }
.callout-note { border-left-color: var(--info); }
.callout-note .callout-title { color: var(--info); }
.callout-info { border-left-color: var(--info); }
.callout-info .callout-title { color: var(--info); }
.callout-tip { border-left-color: var(--accent); }
.callout-tip .callout-title { color: var(--accent-2); }
.callout-warning { border-left-color: var(--warn); }
.callout-warning .callout-title { color: var(--warn); }
.callout-danger { border-left-color: var(--danger); }
.callout-danger .callout-title { color: var(--danger); }

/* pager */
.pager-nav { display: flex; gap: 14px; margin: 48px 0 0; }
.pager { flex: 1; display: flex; flex-direction: column; gap: 4px; padding: 16px 18px; border: 1px solid var(--border); border-radius: var(--radius); background: var(--bg-elev); min-width: 0; }
.pager:hover { text-decoration: none; border-color: var(--border-strong); background: var(--bg-elev-2); }
.pager-next { text-align: right; align-items: flex-end; }
.pager-dir { font-size: 12.5px; color: var(--fg-faint); }
.pager-title { font-weight: 600; color: var(--fg); font-size: 15px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; max-width: 100%; }

.doc-footer { margin-top: 48px; padding-top: 24px; border-top: 1px solid var(--border); color: var(--fg-muted); font-size: 13.5px; }
.doc-footer p { margin: 0 0 6px; }

/* TOC */
.toc { position: sticky; top: 84px; align-self: flex-start; width: var(--toc-w); flex: none; max-height: calc(100vh - 110px); overflow-y: auto; font-size: 13.5px; }
.toc-title { font-size: 11px; text-transform: uppercase; letter-spacing: 0.08em; color: var(--fg-faint); font-weight: 700; margin: 0 0 10px; }
.toc ul { list-style: none; margin: 0; padding: 0; border-left: 1px solid var(--border); }
.toc li a { display: block; padding: 4px 0 4px 14px; color: var(--fg-muted); margin-left: -1px; border-left: 2px solid transparent; }
.toc li a:hover { color: var(--fg); text-decoration: none; }
.toc li a.active { color: var(--accent-2); border-left-color: var(--accent); }
.toc-l3 a { padding-left: 26px; font-size: 13px; }

/* ---------- search modal -------------------------------------------------- */
.search-modal { position: fixed; inset: 0; z-index: 100; background: rgba(0, 0, 0, 0.55); display: flex; align-items: flex-start; justify-content: center; padding: 10vh 16px 16px; }
.search-modal[hidden] { display: none; }
.search-panel { width: 100%; max-width: 640px; background: var(--bg-elev); border: 1px solid var(--border-strong); border-radius: var(--radius); box-shadow: var(--shadow); overflow: hidden; }
#search-input { width: 100%; padding: 18px 20px; font-size: 17px; border: none; border-bottom: 1px solid var(--border); background: transparent; color: var(--fg); font-family: inherit; }
#search-input:focus { outline: none; }
.search-results { list-style: none; margin: 0; padding: 8px; max-height: 52vh; overflow-y: auto; }
.search-results:empty { display: none; }
.search-results li a { display: block; padding: 11px 14px; border-radius: var(--radius-sm); color: var(--fg); }
.search-results li a:hover, .search-results li a.active { background: var(--accent-soft); text-decoration: none; }
.sr-section { font-size: 11.5px; color: var(--accent-2); text-transform: uppercase; letter-spacing: 0.05em; font-weight: 700; }
.sr-title { font-weight: 600; font-size: 15px; margin: 2px 0; }
.sr-snippet { font-size: 13px; color: var(--fg-muted); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.sr-snippet mark, .sr-title mark { background: var(--accent-soft); color: var(--accent-2); border-radius: 3px; padding: 0 2px; }
.search-empty { padding: 24px; text-align: center; color: var(--fg-muted); font-size: 14px; }
.search-hint { display: flex; gap: 6px; align-items: center; padding: 10px 16px; border-top: 1px solid var(--border); color: var(--fg-faint); font-size: 12px; margin: 0; }

/* ---------- responsive ---------------------------------------------------- */
@media (max-width: 1100px) {
  .toc { display: none; }
}
@media (max-width: 860px) {
  .menu-toggle { display: grid; }
  .search-open-label { display: none; }
  .search-open { min-width: 0; }
  .ghost-link { display: none; }
  .sidebar {
    position: fixed; top: 60px; left: 0; z-index: 40; width: 300px; max-width: 84vw;
    background: var(--bg-elev); transform: translateX(-102%); transition: transform 0.22s ease;
    border-right: 1px solid var(--border-strong); box-shadow: var(--shadow);
  }
  body.nav-open .sidebar { transform: translateX(0); }
  body.nav-open .sidebar-scrim { display: block; position: fixed; inset: 60px 0 0 0; z-index: 39; background: rgba(0,0,0,0.5); }
  .layout { display: block; }
  .doc { padding: 24px 16px 64px; }
  .landing { padding: 0 16px; }
  .hero { padding: 48px 0 32px; }
  .chain-strip { grid-template-columns: repeat(2, 1fr); }
  .pager-nav { flex-direction: column; }
}
@media (max-width: 420px) {
  body { font-size: 15.5px; }
  .chain-strip { grid-template-columns: 1fr; }
  .card-grid { grid-template-columns: 1fr; }
  .hero h1 { font-size: 34px; }
}