/* Learning site: tokens first, then layout, then content. */
:root {
  --bg: #faf9f5;
  --surface: #ffffff;
  --surface-2: #f3f1ea;
  --ink: #1f1e1c;
  --ink-2: #5d5b55;
  --ink-3: #8a877f;
  --line: #e4e1d8;
  --line-2: #d3cfc3;
  --brand: #c96442;
  --brand-soft: rgba(201, 100, 66, 0.1);
  --link: #2f5fd0;
  --code-bg: #f1eee6;
  --shadow: 0 1px 2px rgba(31, 30, 28, 0.05), 0 4px 16px rgba(31, 30, 28, 0.05);

  /* Chart tokens used by the doc's diagrams */
  --cds-text-primary: #1f1e1c;
  --cds-text-secondary: #67645d;
  --cds-chart-axis: #8f8b82;
  --cds-chart-grid: #e2ded3;
  --cds-chart-muted: #b9b5ab;
  --cds-chart-categorical-1: #2f6fe4;
  --cds-chart-categorical-2: #d9822b;
  --cds-chart-reference: #8f8b82;
  --cds-chart-reference-tint: rgba(31, 30, 28, 0.05);
  --cds-chart-status-critical: #d24a3c;
  --cds-chart-status-warning: #d99a1e;

  --sans: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --serif: "Iowan Old Style", "Palatino Linotype", Palatino, Charter, "Source Serif Pro", Georgia, serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
  --top: 56px;
  --side: 272px;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #1c1b19; --surface: #242320; --surface-2: #2b2a26; --ink: #ecebe6; --ink-2: #b5b2a9; --ink-3: #8c897f;
    --line: #36342f; --line-2: #45433d; --brand: #e07a56; --brand-soft: rgba(224, 122, 86, 0.14); --link: #8fb0ff; --code-bg: #2b2a26;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 4px 16px rgba(0, 0, 0, 0.25);
    --cds-text-primary: #ecebe6; --cds-text-secondary: #a9a69d; --cds-chart-axis: #8a877e; --cds-chart-grid: #3a3833;
    --cds-chart-muted: #6c6961; --cds-chart-categorical-1: #6f9dff; --cds-chart-categorical-2: #f0a35a; --cds-chart-reference: #8a877e;
    --cds-chart-reference-tint: rgba(255, 255, 255, 0.06); --cds-chart-status-critical: #ff7a6b; --cds-chart-status-warning: #f0b84a;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #1c1b19; --surface: #242320; --surface-2: #2b2a26; --ink: #ecebe6; --ink-2: #b5b2a9; --ink-3: #8c897f;
  --line: #36342f; --line-2: #45433d; --brand: #e07a56; --brand-soft: rgba(224, 122, 86, 0.14); --link: #8fb0ff; --code-bg: #2b2a26;
  --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 4px 16px rgba(0, 0, 0, 0.25);
  --cds-text-primary: #ecebe6; --cds-text-secondary: #a9a69d; --cds-chart-axis: #8a877e; --cds-chart-grid: #3a3833;
  --cds-chart-muted: #6c6961; --cds-chart-categorical-1: #6f9dff; --cds-chart-categorical-2: #f0a35a; --cds-chart-reference: #8a877e;
  --cds-chart-reference-tint: rgba(255, 255, 255, 0.06); --cds-chart-status-critical: #ff7a6b; --cds-chart-status-warning: #f0b84a;
  color-scheme: dark;
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-padding-top: calc(var(--top) + 16px); }
body {
  margin: 0; background: var(--bg); color: var(--ink);
  font: 16px/1.65 var(--sans); -webkit-font-smoothing: antialiased;
}
a { color: var(--link); text-underline-offset: 2px; text-decoration-thickness: 1px; }
a:hover { text-decoration-thickness: 2px; }
:focus-visible { outline: 2px solid var(--brand); outline-offset: 2px; border-radius: 4px; }

.skip { position: absolute; left: -999px; top: 8px; background: var(--surface); padding: 8px 12px; z-index: 100; }
.skip:focus { left: 8px; }

/* ---------- top bar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 30; height: var(--top);
  display: flex; align-items: center; gap: 10px; padding: 0 16px;
  background: color-mix(in srgb, var(--bg) 86%, transparent);
  backdrop-filter: saturate(1.4) blur(10px); -webkit-backdrop-filter: saturate(1.4) blur(10px);
  border-bottom: 1px solid var(--line);
}
.brand { display: inline-flex; align-items: center; gap: 10px; color: var(--ink); text-decoration: none; font-weight: 650; letter-spacing: -0.01em; }
.mark {
  width: 28px; height: 28px; border-radius: 8px; display: grid; place-items: center;
  background: var(--brand); color: #fff; font: 700 15px/1 var(--serif);
}
.crumb { color: var(--ink-3); font-size: 14px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; min-width: 0; }
.crumb::before { content: "/"; margin-right: 10px; color: var(--line-2); }
.icon-btn {
  display: inline-grid; place-items: center; width: 38px; height: 38px; border-radius: 10px;
  border: 1px solid transparent; background: none; color: var(--ink-2); cursor: pointer;
}
.icon-btn:hover { background: var(--surface-2); color: var(--ink); }
.theme-btn { margin-left: auto; }
.theme-btn .moon { display: none; }
:root[data-theme="dark"] .theme-btn .sun { display: none; }
:root[data-theme="dark"] .theme-btn .moon { display: block; }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .theme-btn .sun { display: none; }
  :root:not([data-theme="light"]) .theme-btn .moon { display: block; }
}

/* ---------- layout ---------- */
.layout { display: block; }
.main { min-width: 0; padding: 24px 16px 40px; }
.sidebar {
  position: fixed; z-index: 40; top: 0; bottom: 0; left: 0; width: min(86vw, 320px);
  background: var(--surface); border-right: 1px solid var(--line);
  padding: 20px 14px 32px; overflow-y: auto; transform: translateX(-105%);
  transition: transform 0.22s ease; box-shadow: var(--shadow);
}
body.nav-open .sidebar { transform: none; }
.scrim { position: fixed; inset: 0; z-index: 35; background: rgba(0, 0, 0, 0.35); }
body.nav-open { overflow: hidden; }

.side-home {
  display: block; padding: 8px 12px; margin-bottom: 8px; border-radius: 8px;
  color: var(--ink-2); text-decoration: none; font-size: 14px; font-weight: 600;
}
.side-home:hover, .side-home.active { background: var(--surface-2); color: var(--ink); }
.side-list, .toc { list-style: none; margin: 0; padding: 0; }
.side-list > li > a {
  display: block; padding: 8px 12px; border-radius: 8px; color: var(--ink); text-decoration: none; font-size: 15px;
}
.side-list > li > a:hover { background: var(--surface-2); }
.side-list > li.active > a { background: var(--brand-soft); color: var(--brand); font-weight: 600; }
.toc { margin: 4px 0 10px 14px; border-left: 1px solid var(--line); }
.toc a {
  display: block; padding: 4px 10px; color: var(--ink-2); text-decoration: none; font-size: 13.5px; line-height: 1.4;
  border-left: 2px solid transparent; margin-left: -1px;
}
.toc a:hover { color: var(--ink); }
.toc a.on { color: var(--brand); border-left-color: var(--brand); }

@media (min-width: 1000px) {
  .menu-btn { display: none; }
  .layout { display: grid; grid-template-columns: var(--side) minmax(0, 1fr); }
  .sidebar {
    position: sticky; top: var(--top); height: calc(100vh - var(--top)); width: auto;
    transform: none; box-shadow: none; background: transparent; z-index: 1; transition: none;
  }
  .scrim { display: none !important; }
  body.nav-open { overflow: auto; }
  .main { padding: 40px 48px 64px; }
}

/* ---------- landing ---------- */
.hero { max-width: 760px; margin: 8px auto 28px; }
.eyebrow { margin: 0 0 6px; color: var(--brand); font-size: 13px; font-weight: 650; letter-spacing: 0.06em; text-transform: uppercase; }
.hero h1 { font: 600 clamp(36px, 7vw, 56px)/1.05 var(--serif); letter-spacing: -0.02em; margin: 0 0 14px; }
.lede { color: var(--ink-2); font-size: 18px; margin: 0; }
.cards { max-width: 1040px; margin: 0 auto; display: grid; gap: 14px; grid-template-columns: 1fr; }
@media (min-width: 640px) { .cards { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 1240px) { .cards { grid-template-columns: repeat(3, 1fr); } }
.card {
  position: relative; display: flex; flex-direction: column; gap: 8px; padding: 20px 20px 18px;
  background: var(--surface); border: 1px solid var(--line); border-radius: 14px;
  color: var(--ink); text-decoration: none; box-shadow: var(--shadow);
  transition: border-color 0.15s, transform 0.15s;
}
.card:hover { border-color: var(--brand); transform: translateY(-2px); }
.card .num { font: 600 13px/1 var(--mono); color: var(--brand); }
.card h2 { margin: 0; font: 600 21px/1.25 var(--serif); letter-spacing: -0.01em; }
.card p { margin: 0; color: var(--ink-2); font-size: 14.5px; line-height: 1.55; flex: 1; }
.card .stats { color: var(--ink-3); font-size: 12.5px; }

/* ---------- article ---------- */
.prose { max-width: 820px; margin: 0 auto; }
.prose h1 { font: 600 clamp(32px, 6vw, 46px)/1.1 var(--serif); letter-spacing: -0.02em; margin: 0 0 8px; }
.prose .meta { color: var(--ink-3); font-size: 14px; margin: 0 0 28px; }
.prose h2 {
  font: 600 clamp(23px, 4vw, 28px)/1.25 var(--serif); letter-spacing: -0.01em;
  margin: 52px 0 14px; padding-top: 18px; border-top: 1px solid var(--line);
}
.prose h3 { font-size: 18px; line-height: 1.35; margin: 32px 0 10px; }
.prose h2, .prose h3 { position: relative; }
.anchor { margin-left: 8px; color: var(--ink-3); text-decoration: none; opacity: 0; font-weight: 400; }
h2:hover .anchor, h3:hover .anchor, .anchor:focus { opacity: 1; }
.prose p, .prose ul, .prose ol { margin: 0 0 16px; }
.prose ul, .prose ol { padding-left: 1.4em; }
.prose li { margin: 4px 0; }
.prose li > p { margin: 0; }
.prose strong { font-weight: 650; }
.prose blockquote { margin: 0 0 16px; padding: 4px 16px; border-left: 3px solid var(--brand); color: var(--ink-2); }
.prose hr { border: 0; border-top: 1px solid var(--line); margin: 32px 0; }

.prose code {
  font: 0.88em/1.5 var(--mono); background: var(--code-bg); padding: 0.12em 0.36em; border-radius: 5px;
  overflow-wrap: anywhere;
}
.prose pre {
  position: relative; margin: 0 0 18px; padding: 16px 18px; background: var(--code-bg);
  border: 1px solid var(--line); border-radius: 12px; overflow-x: auto;
}
.prose pre code { background: none; padding: 0; font-size: 13.5px; overflow-wrap: normal; white-space: pre; }
.copy {
  position: absolute; top: 8px; right: 8px; font: 600 12px var(--sans); color: var(--ink-2);
  background: var(--surface); border: 1px solid var(--line); border-radius: 7px; padding: 4px 9px; cursor: pointer;
  opacity: 0.85;
}
.copy:hover { opacity: 1; color: var(--ink); }

.table-wrap {
  margin: 0 0 20px; overflow-x: auto; border: 1px solid var(--line); border-radius: 12px; background: var(--surface);
  -webkit-overflow-scrolling: touch;
}
.prose table { width: 100%; border-collapse: collapse; font-size: 14.5px; line-height: 1.5; }
.prose th, .prose td { text-align: left; vertical-align: top; padding: 10px 14px; border-bottom: 1px solid var(--line); }
.prose th { background: var(--surface-2); font-weight: 650; font-size: 13.5px; white-space: nowrap; }
.prose tr:last-child td { border-bottom: 0; }
.prose td p { margin: 0; }
@media (max-width: 640px) {
  .prose table { font-size: 13.5px; }
  .prose th, .prose td { padding: 9px 11px; min-width: 120px; }
}

.viz { margin: 8px 0 28px; }
.viz-scroll {
  overflow-x: auto; background: var(--surface); border: 1px solid var(--line); border-radius: 14px; padding: 12px;
  -webkit-overflow-scrolling: touch;
}
.viz svg { display: block; width: 100%; height: auto; min-width: 600px; font-family: var(--sans); }
@media (min-width: 700px) { .viz svg { min-width: 0; } }
.viz figcaption { margin-top: 8px; color: var(--ink-3); font-size: 13px; text-align: center; }
.viz-missing { padding: 32px; text-align: center; color: var(--ink-3); border: 1px dashed var(--line-2); border-radius: 14px; }

li.task { list-style: none; margin-left: -1.2em; }
li.task .box {
  display: inline-block; width: 15px; height: 15px; margin-right: 8px; vertical-align: -2px;
  border: 1.5px solid var(--ink-3); border-radius: 4px;
}
li.task.done .box { background: var(--brand); border-color: var(--brand); }

.pager { max-width: 820px; margin: 56px auto 0; display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.pager a {
  display: flex; flex-direction: column; gap: 2px; padding: 14px 16px; border: 1px solid var(--line);
  border-radius: 12px; background: var(--surface); color: var(--ink); text-decoration: none; font-weight: 600;
}
.pager a:hover { border-color: var(--brand); }
.pager a span { color: var(--ink-3); font-size: 12.5px; font-weight: 500; }
.pager .next { text-align: right; }

.footer { max-width: 820px; margin: 40px auto 0; color: var(--ink-3); font-size: 13px; text-align: center; }

@media (prefers-reduced-motion: reduce) { * { transition: none !important; } }
@media print {
  .topbar, .sidebar, .pager, .copy, .scrim { display: none !important; }
  .layout { display: block; }
  .viz svg { min-width: 0; }
}

/* Wide diagrams on phones: show a hint that they scroll sideways. */
.viz.scrollable .viz-scroll { mask-image: linear-gradient(to right, #000 85%, transparent); -webkit-mask-image: linear-gradient(to right, #000 85%, transparent); }
.viz.scrollable.at-end .viz-scroll { mask-image: none; -webkit-mask-image: none; }
.viz.scrollable figcaption::after { content: " · swipe to see all"; color: var(--brand); }