/* ==========================================================================
   Learn BRUTAL GL — design tokens
   ========================================================================== */
:root {
  --bg: #fbfaff;
  --bg-2: #f3f1fa;
  --surface: #ffffff;
  --surface-2: #f6f4fc;
  --border: #e4e0f0;
  --border-strong: #cfc8e3;
  --text: #1b1530;
  --text-2: #4c4566;
  --text-3: #7a7392;
  --accent: #7c3aed;
  --accent-2: #a855f7;
  --accent-soft: #efe7ff;
  --accent-ink: #5b21b6;
  --gl: #0ea5e9;          /* OpenGL colour */
  --gl-soft: #e0f4fd;
  --vk: #dc2626;          /* Vulkan colour */
  --vk-soft: #fde8e8;
  --ok: #16a34a;
  --ok-soft: #e3f6ea;
  --warn: #b45309;
  --warn-soft: #fdf1dc;
  --code-bg: #f7f5fd;
  --code-text: #2a2340;
  --tok-kw: #7c3aed;
  --tok-type: #0369a1;
  --tok-str: #15803d;
  --tok-num: #c2410c;
  --tok-com: #8a84a0;
  --tok-fn: #b91c5c;
  --tok-pre: #a16207;
  --shadow-sm: 0 1px 2px rgba(30, 20, 60, .06), 0 1px 3px rgba(30, 20, 60, .06);
  --shadow: 0 6px 24px -8px rgba(40, 20, 90, .18), 0 2px 6px rgba(40, 20, 90, .06);
  --shadow-lg: 0 24px 60px -20px rgba(40, 20, 90, .35);
  --radius: 14px;
  --radius-sm: 9px;
  --topbar-h: 60px;
  --sidebar-w: 280px;
  --toc-w: 230px;
  --font: 'Inter', ui-sans-serif, system-ui, -apple-system, 'Segoe UI', sans-serif;
  --mono: 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --ease: cubic-bezier(.2, .8, .2, 1);
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0c0a14;
    --bg-2: #120f1d;
    --surface: #151223;
    --surface-2: #1b172c;
    --border: #2a2540;
    --border-strong: #3a3356;
    --text: #ece9f7;
    --text-2: #b7b0cf;
    --text-3: #847c9f;
    --accent: #a78bfa;
    --accent-2: #c084fc;
    --accent-soft: #261c42;
    --accent-ink: #d8ccff;
    --gl: #38bdf8;
    --gl-soft: #0f2a3a;
    --vk: #f87171;
    --vk-soft: #3a1518;
    --ok: #4ade80;
    --ok-soft: #10301d;
    --warn: #fbbf24;
    --warn-soft: #33260a;
    --code-bg: #110e1c;
    --code-text: #e4def7;
    --tok-kw: #c4a5ff;
    --tok-type: #7dd3fc;
    --tok-str: #86efac;
    --tok-num: #fdba74;
    --tok-com: #6f6889;
    --tok-fn: #f9a8d4;
    --tok-pre: #fcd34d;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, .4);
    --shadow: 0 8px 28px -10px rgba(0, 0, 0, .7), 0 2px 6px rgba(0, 0, 0, .3);
    --shadow-lg: 0 30px 70px -20px rgba(0, 0, 0, .8);
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0c0a14;
  --bg-2: #120f1d;
  --surface: #151223;
  --surface-2: #1b172c;
  --border: #2a2540;
  --border-strong: #3a3356;
  --text: #ece9f7;
  --text-2: #b7b0cf;
  --text-3: #847c9f;
  --accent: #a78bfa;
  --accent-2: #c084fc;
  --accent-soft: #261c42;
  --accent-ink: #d8ccff;
  --gl: #38bdf8;
  --gl-soft: #0f2a3a;
  --vk: #f87171;
  --vk-soft: #3a1518;
  --ok: #4ade80;
  --ok-soft: #10301d;
  --warn: #fbbf24;
  --warn-soft: #33260a;
  --code-bg: #110e1c;
  --code-text: #e4def7;
  --tok-kw: #c4a5ff;
  --tok-type: #7dd3fc;
  --tok-str: #86efac;
  --tok-num: #fdba74;
  --tok-com: #6f6889;
  --tok-fn: #f9a8d4;
  --tok-pre: #fcd34d;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, .4);
  --shadow: 0 8px 28px -10px rgba(0, 0, 0, .7), 0 2px 6px rgba(0, 0, 0, .3);
  --shadow-lg: 0 30px 70px -20px rgba(0, 0, 0, .8);
  color-scheme: dark;
}

/* ==========================================================================
   Base
   ========================================================================== */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: calc(var(--topbar-h) + 16px); }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.7 var(--font);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  transition: background-color .3s var(--ease), color .3s var(--ease);
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 3px; }
img, svg, canvas { display: block; max-width: 100%; }
button { font: inherit; color: inherit; }
kbd {
  font: 600 11px/1 var(--mono);
  padding: 3px 6px;
  border-radius: 6px;
  border: 1px solid var(--border-strong);
  background: var(--surface-2);
  color: var(--text-2);
}
[hidden] { display: none !important; }
::selection { background: color-mix(in srgb, var(--accent) 30%, transparent); }

/* ==========================================================================
   Top bar
   ========================================================================== */
.progress-bar {
  position: fixed; top: 0; left: 0; height: 3px; width: 0; z-index: 60;
  background: linear-gradient(90deg, var(--gl), var(--accent-2), var(--vk));
  transition: width .1s linear;
}
.topbar {
  position: sticky; top: 0; z-index: 50;
  height: var(--topbar-h);
  display: flex; align-items: center; gap: 16px;
  padding: 0 20px;
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: saturate(1.6) blur(14px);
  -webkit-backdrop-filter: saturate(1.6) blur(14px);
  border-bottom: 1px solid var(--border);
}
.brand { display: flex; align-items: center; gap: 10px; color: var(--text); font-weight: 600; letter-spacing: -.01em; }
.brand:hover { text-decoration: none; }
.brand-mark { transition: transform .5s var(--ease); }
.brand:hover .brand-mark { transform: rotate(-12deg) scale(1.08); }
.brand-text b { font-weight: 800; background: linear-gradient(90deg, var(--accent), var(--vk)); -webkit-background-clip: text; background-clip: text; color: transparent; margin: 0 1px; }
.search-trigger {
  display: flex; align-items: center; gap: 10px;
  margin-left: 12px; padding: 7px 10px 7px 12px; min-width: 260px;
  border: 1px solid var(--border); border-radius: 10px;
  background: var(--surface); color: var(--text-3); cursor: pointer; font-size: 14px;
  transition: border-color .2s, box-shadow .2s;
}
.search-trigger:hover { border-color: var(--accent); box-shadow: 0 0 0 4px var(--accent-soft); }
.search-trigger span { flex: 1; text-align: left; }
.top-links { margin-left: auto; display: flex; gap: 18px; font-size: 14px; font-weight: 500; }
.top-links a { color: var(--text-2); }
.top-links a:hover { color: var(--accent); text-decoration: none; }
.theme-switch {
  display: flex; gap: 2px; padding: 3px;
  border: 1px solid var(--border); border-radius: 999px; background: var(--surface);
}
.theme-switch button {
  display: grid; place-items: center; width: 30px; height: 26px;
  border: 0; border-radius: 999px; background: transparent; color: var(--text-3); cursor: pointer;
  transition: background .2s, color .2s;
}
.theme-switch button:hover { color: var(--text); }
.theme-switch button.active { background: var(--accent); color: #fff; }
.icon-btn { display: grid; place-items: center; width: 38px; height: 38px; border: 0; border-radius: 10px; background: transparent; cursor: pointer; }
.icon-btn:hover { background: var(--surface-2); }
.only-mobile { display: none; }
.scrim { display: none; }

/* ==========================================================================
   Layout
   ========================================================================== */
.layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) minmax(0, 1fr) var(--toc-w);
  min-height: calc(100vh - var(--topbar-h));
}
.layout.no-toc { grid-template-columns: var(--sidebar-w) minmax(0, 1fr); }
.layout.no-toc .toc { display: none; }

.sidebar {
  position: sticky; top: var(--topbar-h);
  height: calc(100vh - var(--topbar-h));
  overflow-y: auto; overscroll-behavior: contain;
  padding: 18px 14px 24px;
  border-right: 1px solid var(--border);
  background: var(--bg);
  display: flex; flex-direction: column; gap: 14px;
  scrollbar-width: thin;
}
.sidebar-progress { padding: 12px; border: 1px solid var(--border); border-radius: var(--radius-sm); background: var(--surface); }
.sp-label { display: flex; justify-content: space-between; font-size: 12px; font-weight: 600; color: var(--text-2); margin-bottom: 8px; }
.sp-track { height: 6px; border-radius: 99px; background: var(--surface-2); overflow: hidden; }
.sp-fill { height: 100%; width: 0; border-radius: 99px; background: linear-gradient(90deg, var(--accent), var(--accent-2)); transition: width .6s var(--ease); }

.nav-group { margin-bottom: 6px; }
.nav-group-title {
  display: flex; align-items: center; gap: 8px; width: 100%;
  padding: 6px 10px; border: 0; background: none; cursor: pointer;
  font-size: 11.5px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; color: var(--text-3);
}
.nav-group-title .chev { margin-left: auto; transition: transform .25s var(--ease); }
.nav-group.collapsed .chev { transform: rotate(-90deg); }
.nav-group ul { list-style: none; margin: 2px 0 0; padding: 0; overflow: hidden; transition: max-height .35s var(--ease); }
.nav-group.collapsed ul { max-height: 0 !important; }
.nav-link {
  position: relative; display: flex; align-items: center; gap: 10px;
  padding: 7px 10px; border-radius: 8px;
  color: var(--text-2); font-size: 14px; font-weight: 500; line-height: 1.35;
  transition: background .15s, color .15s, transform .15s;
}
.nav-link:hover { background: var(--surface-2); color: var(--text); text-decoration: none; }
.nav-link.active { background: var(--accent-soft); color: var(--accent-ink); font-weight: 600; }
.nav-link.active::before { content: ''; position: absolute; left: -14px; top: 8px; bottom: 8px; width: 3px; border-radius: 3px; background: var(--accent); }
.nav-num {
  flex: none; display: grid; place-items: center; width: 22px; height: 22px;
  border-radius: 50%; border: 1.5px solid var(--border-strong);
  font-size: 10.5px; font-weight: 700; color: var(--text-3);
  transition: all .3s var(--ease);
}
.nav-link.done .nav-num { background: var(--ok); border-color: var(--ok); color: #fff; }
.nav-link.done .nav-num span { display: none; }
.nav-link.done .nav-num::after { content: '✓'; font-size: 12px; }
.sidebar-foot { margin-top: auto; padding-top: 12px; border-top: 1px solid var(--border); }

.switch-row { display: flex; align-items: center; gap: 10px; cursor: pointer; font-size: 14px; font-weight: 500; color: var(--text-2); user-select: none; }
.switch-row input { position: absolute; opacity: 0; pointer-events: none; }
.switch { position: relative; width: 36px; height: 20px; border-radius: 99px; background: var(--border-strong); transition: background .25s; flex: none; }
.switch::after { content: ''; position: absolute; top: 2px; left: 2px; width: 16px; height: 16px; border-radius: 50%; background: #fff; box-shadow: var(--shadow-sm); transition: transform .25s var(--ease); }
.switch-row input:checked + .switch { background: var(--vk); }
.switch-row input:checked + .switch::after { transform: translateX(16px); }
.switch-row input:focus-visible + .switch { outline: 2px solid var(--accent); outline-offset: 2px; }

.content { min-width: 0; padding: 40px clamp(20px, 4vw, 56px) 80px; outline: none; }
.toc {
  position: sticky; top: var(--topbar-h);
  height: calc(100vh - var(--topbar-h));
  overflow-y: auto; padding: 40px 20px 20px 4px; font-size: 13px;
}
.toc h4 { margin: 0 0 10px; font-size: 11.5px; letter-spacing: .08em; text-transform: uppercase; color: var(--text-3); }
.toc ul { list-style: none; margin: 0; padding: 0; border-left: 1px solid var(--border); }
.toc a { display: block; padding: 4px 0 4px 14px; margin-left: -1px; border-left: 2px solid transparent; color: var(--text-3); line-height: 1.4; transition: color .2s, border-color .2s; }
.toc a:hover { color: var(--text); text-decoration: none; }
.toc a.active { color: var(--accent); border-left-color: var(--accent); font-weight: 600; }
.toc a.vk-link { color: var(--vk); opacity: .8; }
.toc-actions { margin-top: 18px; display: flex; flex-direction: column; gap: 8px; }

/* ==========================================================================
   Article typography
   ========================================================================== */
.article { max-width: 780px; margin: 0 auto; }
.page-enter { animation: pageIn .5s var(--ease) both; }
@keyframes pageIn { from { opacity: 0; transform: translateY(14px); } to { opacity: 1; transform: none; } }

.crumbs { display: flex; gap: 8px; align-items: center; font-size: 13px; color: var(--text-3); margin-bottom: 12px; }
.chip {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 3px 10px; border-radius: 99px; font-size: 12px; font-weight: 600;
  background: var(--surface-2); color: var(--text-2); border: 1px solid var(--border);
}
.chip.gl { background: var(--gl-soft); color: var(--gl); border-color: transparent; }
.chip.vk { background: var(--vk-soft); color: var(--vk); border-color: transparent; }
.chip.accent { background: var(--accent-soft); color: var(--accent-ink); border-color: transparent; }
.article h1 {
  font-size: clamp(32px, 5vw, 46px); line-height: 1.1; letter-spacing: -.035em; font-weight: 800;
  margin: 0 0 14px;
}
.article .lede { font-size: 19px; color: var(--text-2); margin: 0 0 22px; line-height: 1.6; }
.meta-row { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 34px; }
.article h2 {
  font-size: 27px; letter-spacing: -.02em; line-height: 1.25; font-weight: 750;
  margin: 56px 0 14px; padding-top: 8px;
}
.article h3 { font-size: 20px; letter-spacing: -.01em; margin: 34px 0 10px; font-weight: 700; }
.article h2 .anchor, .article h3 .anchor { opacity: 0; margin-left: 8px; color: var(--text-3); font-weight: 400; transition: opacity .2s; }
.article h2:hover .anchor, .article h3:hover .anchor { opacity: 1; }
.article p { margin: 0 0 16px; }
.article ul, .article ol { padding-left: 22px; margin: 0 0 18px; }
.article li { margin: 6px 0; }
.article li::marker { color: var(--accent); }
.article strong { font-weight: 650; color: var(--text); }
.article :not(pre) > code {
  font: 500 .86em var(--mono);
  padding: 2px 6px; border-radius: 6px;
  background: var(--surface-2); border: 1px solid var(--border); color: var(--accent-ink);
  white-space: nowrap;
}
.article hr { border: 0; height: 1px; background: var(--border); margin: 40px 0; }
.article table { width: 100%; border-collapse: separate; border-spacing: 0; margin: 0 0 22px; font-size: 14.5px; border: 1px solid var(--border); border-radius: var(--radius-sm); overflow: hidden; }
.article th, .article td { padding: 10px 14px; text-align: left; vertical-align: top; border-bottom: 1px solid var(--border); }
.article th { background: var(--surface-2); font-weight: 650; font-size: 13px; }
.article tr:last-child td { border-bottom: 0; }
.article td code { white-space: normal !important; }
.table-scroll { overflow-x: auto; margin-bottom: 22px; }
.table-scroll table { margin: 0; }

.term { border-bottom: 1.5px dotted var(--accent); cursor: help; }
.term-tip {
  position: fixed; z-index: 80; max-width: 320px;
  padding: 12px 14px; border-radius: 12px;
  background: var(--surface); border: 1px solid var(--border-strong); box-shadow: var(--shadow-lg);
  font-size: 13.5px; line-height: 1.55; color: var(--text-2);
  animation: tipIn .18s var(--ease);
  pointer-events: none;
}
.term-tip b { display: block; color: var(--text); margin-bottom: 4px; font-size: 14px; }
@keyframes tipIn { from { opacity: 0; transform: translateY(4px); } }

/* Scroll reveal */
.reveal { opacity: 0; transform: translateY(18px); transition: opacity .6s var(--ease), transform .6s var(--ease); }
.reveal.in { opacity: 1; transform: none; }
@media (prefers-reduced-motion: reduce) {
  .reveal { opacity: 1; transform: none; transition: none; }
  .page-enter { animation: none; }
  html { scroll-behavior: auto; }
}

/* ==========================================================================
   Callouts
   ========================================================================== */
.callout {
  position: relative; display: flex; gap: 14px;
  padding: 16px 18px; margin: 22px 0; border-radius: var(--radius);
  background: var(--surface-2); border: 1px solid var(--border);
}
.callout .c-icon { flex: none; width: 30px; height: 30px; display: grid; place-items: center; border-radius: 9px; font-size: 16px; background: var(--surface); }
.callout .c-body { min-width: 0; }
.callout .c-body > :last-child { margin-bottom: 0; }
.callout .c-title { font-weight: 700; margin-bottom: 4px; font-size: 15px; }
.callout.tip { background: var(--ok-soft); border-color: color-mix(in srgb, var(--ok) 30%, transparent); }
.callout.tip .c-title { color: var(--ok); }
.callout.warn { background: var(--warn-soft); border-color: color-mix(in srgb, var(--warn) 30%, transparent); }
.callout.warn .c-title { color: var(--warn); }
.callout.eli5 { background: var(--accent-soft); border-color: color-mix(in srgb, var(--accent) 30%, transparent); }
.callout.eli5 .c-title { color: var(--accent-ink); }
.callout.gl { background: var(--gl-soft); border-color: color-mix(in srgb, var(--gl) 30%, transparent); }
.callout.gl .c-title { color: var(--gl); }

/* ==========================================================================
   Code blocks
   ========================================================================== */
.code {
  margin: 20px 0 24px; border-radius: var(--radius);
  background: var(--code-bg); border: 1px solid var(--border);
  overflow: hidden; box-shadow: var(--shadow-sm);
}
.code-head {
  display: flex; align-items: center; gap: 4px;
  padding: 6px 8px 0; border-bottom: 1px solid var(--border);
  background: color-mix(in srgb, var(--surface-2) 70%, var(--code-bg));
}
.code-tab {
  position: relative; padding: 8px 12px 10px; border: 0; background: none; cursor: pointer;
  font: 600 12.5px var(--font); color: var(--text-3);
  display: flex; align-items: center; gap: 7px;
}
.code-tab:hover { color: var(--text); }
.code-tab.active { color: var(--text); }
.code-tab.active::after { content: ''; position: absolute; left: 10px; right: 10px; bottom: -1px; height: 2px; border-radius: 2px; background: var(--accent); }
.code-tab .dot { width: 8px; height: 8px; border-radius: 50%; background: var(--text-3); }
.code-tab .dot.cs { background: #a855f7; }
.code-tab .dot.glsl { background: var(--gl); }
.code-tab .dot.vk { background: var(--vk); }
.code-tab .dot.sh { background: var(--ok); }
.code-actions { margin-left: auto; display: flex; gap: 4px; padding-bottom: 6px; }
.code-btn {
  padding: 4px 9px; border-radius: 7px; border: 1px solid var(--border); background: var(--surface);
  font: 600 11.5px var(--font); color: var(--text-2); cursor: pointer; transition: all .15s;
}
.code-btn:hover { color: var(--accent); border-color: var(--accent); }
.code-btn.ok { color: var(--ok); border-color: var(--ok); }
.code pre {
  margin: 0; padding: 16px 18px; overflow-x: auto;
  font: 13.4px/1.65 var(--mono); color: var(--code-text);
  tab-size: 4; scrollbar-width: thin;
}
.code pre.hidden { display: none; }
.code pre .ln { display: inline-block; width: 2.2em; margin-left: -.4em; color: var(--tok-com); opacity: .55; user-select: none; text-align: right; padding-right: 1em; }
.code pre .hl-line { display: inline-block; width: calc(100% + 36px); margin: 0 -18px; padding: 0 18px; background: color-mix(in srgb, var(--accent) 12%, transparent); box-shadow: inset 3px 0 0 var(--accent); }
.code .tok-kw { color: var(--tok-kw); font-weight: 600; }
.code .tok-type { color: var(--tok-type); }
.code .tok-str { color: var(--tok-str); }
.code .tok-num { color: var(--tok-num); }
.code .tok-com { color: var(--tok-com); font-style: italic; }
.code .tok-fn { color: var(--tok-fn); }
.code .tok-pre { color: var(--tok-pre); }
.code-caption { padding: 8px 18px 10px; font-size: 13px; color: var(--text-3); border-top: 1px solid var(--border); }

/* ==========================================================================
   Vulkan Corner
   ========================================================================== */
.vk-corner {
  position: relative; margin: 44px 0 28px; padding: 0;
  border-radius: 18px; overflow: hidden;
  background: linear-gradient(135deg, color-mix(in srgb, var(--vk) 9%, var(--surface)), var(--surface) 55%);
  border: 1px solid color-mix(in srgb, var(--vk) 35%, var(--border));
  box-shadow: var(--shadow);
}
body.no-vk .vk-corner, body.no-vk .vk-only { display: none; }
.vk-corner > summary {
  list-style: none; cursor: pointer;
  display: flex; align-items: center; gap: 14px; padding: 18px 22px;
}
.vk-corner > summary::-webkit-details-marker { display: none; }
.vk-badge {
  flex: none; width: 42px; height: 42px; border-radius: 12px; display: grid; place-items: center;
  background: var(--vk); color: #fff; font-weight: 800; font-size: 18px; letter-spacing: -.04em;
  box-shadow: 0 6px 18px -6px var(--vk);
}
.vk-corner .vk-title { font-size: 18px; font-weight: 750; letter-spacing: -.01em; margin: 0; }
.vk-corner .vk-sub { font-size: 13.5px; color: var(--text-3); }
.vk-corner .vk-chev { margin-left: auto; transition: transform .3s var(--ease); color: var(--text-3); }
.vk-corner[open] .vk-chev { transform: rotate(180deg); }
.vk-body { padding: 4px 22px 22px; border-top: 1px dashed color-mix(in srgb, var(--vk) 30%, var(--border)); }
.vk-body h4 { margin: 18px 0 8px; font-size: 15.5px; }

.compare { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin: 16px 0; }
.compare > div { padding: 14px 16px; border-radius: 12px; background: var(--surface); border: 1px solid var(--border); font-size: 14.5px; }
.compare > div > :last-child { margin-bottom: 0; }
.compare h5 { margin: 0 0 8px; font-size: 13px; letter-spacing: .04em; text-transform: uppercase; display: flex; align-items: center; gap: 8px; }
.compare .gl-side h5 { color: var(--gl); }
.compare .vk-side h5 { color: var(--vk); }
.compare ul { margin: 0; padding-left: 18px; }

.steps-vs { display: grid; grid-template-columns: 1fr 1fr; gap: 0 16px; margin: 14px 0; font-size: 14px; }
.steps-vs .col h5 { margin: 0 0 8px; font-size: 12.5px; text-transform: uppercase; letter-spacing: .06em; }
.steps-vs .col.gl h5 { color: var(--gl); }
.steps-vs .col.vk h5 { color: var(--vk); }
.steps-vs ol { margin: 0; padding: 0; list-style: none; counter-reset: s; }
.steps-vs li { counter-increment: s; position: relative; padding: 6px 10px 6px 34px; margin: 0 0 6px; border-radius: 9px; background: var(--surface); border: 1px solid var(--border); }
.steps-vs li::before { content: counter(s); position: absolute; left: 8px; top: 7px; width: 18px; height: 18px; border-radius: 50%; display: grid; place-items: center; font-size: 10.5px; font-weight: 700; color: #fff; }
.steps-vs .gl li::before { background: var(--gl); }
.steps-vs .vk li::before { background: var(--vk); }

/* ==========================================================================
   Interactive demo frame
   ========================================================================== */
.demo {
  margin: 28px 0 32px; border-radius: 18px; overflow: hidden;
  border: 1px solid var(--border); background: var(--surface); box-shadow: var(--shadow);
}
.demo-head { display: flex; align-items: center; gap: 10px; padding: 12px 16px; border-bottom: 1px solid var(--border); background: var(--surface-2); }
.demo-head .live { display: inline-flex; align-items: center; gap: 6px; font-size: 11px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; color: var(--ok); }
.demo-head .live::before { content: ''; width: 7px; height: 7px; border-radius: 50%; background: var(--ok); box-shadow: 0 0 0 0 var(--ok); animation: pulse 2s infinite; }
@keyframes pulse { 0% { box-shadow: 0 0 0 0 color-mix(in srgb, var(--ok) 60%, transparent); } 70% { box-shadow: 0 0 0 8px transparent; } 100% { box-shadow: 0 0 0 0 transparent; } }
.demo-head .demo-title { font-weight: 650; font-size: 14.5px; }
.demo-head .demo-hint { margin-left: auto; font-size: 12.5px; color: var(--text-3); }
.demo-body { display: grid; grid-template-columns: minmax(0, 1fr) 260px; }
.demo-body.stack { grid-template-columns: 1fr; }
/* Side by side: the stage fills the row height so tall control panels leave no gap. */
@media (min-width: 981px) {
  .demo-body:not(.stack) .demo-stage { aspect-ratio: auto !important; min-height: 380px; }
}
.demo-stage { position: relative; background: #0b0913; min-height: 260px; }
.demo-stage canvas { position: absolute; inset: 0; width: 100%; height: 100%; display: block; touch-action: none; }
.demo-stage .overlay-label {
  position: absolute; left: 12px; top: 12px; padding: 4px 10px; border-radius: 99px;
  background: rgba(0, 0, 0, .55); color: #fff; font: 600 11.5px var(--font); letter-spacing: .02em;
  backdrop-filter: blur(6px); pointer-events: none;
}
.demo-stage .overlay-label.br { left: auto; top: auto; right: 12px; bottom: 12px; }
.demo-controls { padding: 14px 16px; border-left: 1px solid var(--border); display: flex; flex-direction: column; gap: 14px; font-size: 13.5px; max-height: 520px; overflow-y: auto; }
.demo-body.stack .demo-controls { border-left: 0; border-top: 1px solid var(--border); display: grid; grid-template-columns: repeat(auto-fill, minmax(200px, 1fr)); }
.demo-foot { padding: 12px 16px; border-top: 1px solid var(--border); font-size: 13.5px; color: var(--text-2); background: var(--surface-2); }
.demo-foot code { font-size: 12px !important; }
.demo-error { padding: 30px; color: var(--text-2); text-align: center; }

.ctl label, .ctl .ctl-label { display: flex; justify-content: space-between; align-items: baseline; gap: 8px; font-weight: 600; font-size: 12.5px; color: var(--text-2); margin-bottom: 6px; }
.ctl output { font: 600 12px var(--mono); color: var(--accent); }
.ctl input[type=range] {
  -webkit-appearance: none; appearance: none; width: 100%; height: 6px; border-radius: 99px;
  background: linear-gradient(90deg, var(--accent) var(--p, 50%), var(--border) var(--p, 50%));
  outline: none; cursor: pointer;
}
.ctl input[type=range]::-webkit-slider-thumb { -webkit-appearance: none; width: 16px; height: 16px; border-radius: 50%; background: #fff; border: 2px solid var(--accent); box-shadow: var(--shadow-sm); transition: transform .15s; }
.ctl input[type=range]::-webkit-slider-thumb:hover { transform: scale(1.2); }
.ctl input[type=range]::-moz-range-thumb { width: 14px; height: 14px; border-radius: 50%; background: #fff; border: 2px solid var(--accent); }
.ctl input[type=color] { width: 100%; height: 32px; border: 1px solid var(--border); border-radius: 8px; padding: 2px; background: var(--surface); cursor: pointer; }
.seg { display: flex; flex-wrap: wrap; gap: 4px; padding: 3px; border-radius: 10px; background: var(--surface-2); border: 1px solid var(--border); }
.seg button { flex: 1 1 auto; padding: 5px 8px; border: 0; border-radius: 7px; background: none; cursor: pointer; font-size: 12px; font-weight: 600; color: var(--text-2); transition: all .15s; white-space: nowrap; }
.seg button:hover { color: var(--text); }
.seg button.on { background: var(--surface); color: var(--accent); box-shadow: var(--shadow-sm); }
.ctl .check { display: flex; align-items: center; gap: 9px; font-weight: 500; color: var(--text); cursor: pointer; margin: 0; justify-content: flex-start; }
.ctl .check input { accent-color: var(--accent); width: 15px; height: 15px; }
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  padding: 8px 14px; border-radius: 10px; border: 1px solid var(--border); background: var(--surface);
  font-weight: 600; font-size: 13.5px; cursor: pointer; color: var(--text); transition: all .18s var(--ease);
}
.btn:hover { border-color: var(--accent); color: var(--accent); text-decoration: none; transform: translateY(-1px); }
.btn.primary { background: linear-gradient(135deg, var(--accent), var(--accent-2)); color: #fff; border-color: transparent; box-shadow: 0 8px 20px -8px var(--accent); }
.btn.primary:hover { color: #fff; box-shadow: 0 12px 26px -8px var(--accent); }
.btn.small { padding: 5px 10px; font-size: 12.5px; }
.btn.ok { background: var(--ok); color: #fff; border-color: var(--ok); }

.readout { font: 12px/1.55 var(--mono); background: var(--code-bg); border: 1px solid var(--border); border-radius: 9px; padding: 9px 11px; color: var(--code-text); white-space: pre; overflow-x: auto; }
.matrix { display: inline-grid; gap: 2px 10px; font: 600 12.5px var(--mono); padding: 8px 12px; border-radius: 9px; background: var(--code-bg); border: 1px solid var(--border); position: relative; }
.matrix::before, .matrix::after { content: ''; position: absolute; top: 4px; bottom: 4px; width: 6px; border: 2px solid var(--text-3); }
.matrix::before { left: 3px; border-right: 0; }
.matrix::after { right: 3px; border-left: 0; }
.matrix span { text-align: right; min-width: 3.4em; transition: color .3s; }
.matrix span.hot { color: var(--accent); }

.shader-editor { position: relative; }
.shader-editor textarea {
  width: 100%; min-height: 230px; resize: vertical; display: block;
  padding: 14px 16px; border: 0; border-top: 1px solid var(--border); outline: none;
  font: 13px/1.6 var(--mono); background: var(--code-bg); color: var(--code-text);
  tab-size: 4;
}
.shader-status { padding: 8px 16px; font: 12px var(--mono); border-top: 1px solid var(--border); }
.shader-status.ok { color: var(--ok); background: var(--ok-soft); }
.shader-status.err { color: var(--vk); background: var(--vk-soft); white-space: pre-wrap; }

/* Pipeline diagram */
.pipeline { display: flex; flex-wrap: wrap; gap: 8px; align-items: stretch; margin: 6px 0 0; }
.pipe-stage {
  flex: 1 1 110px; position: relative; padding: 12px 10px; border-radius: 12px; text-align: center;
  border: 1.5px solid var(--border); background: var(--surface); cursor: pointer;
  font-size: 13px; font-weight: 650; transition: all .3s var(--ease);
}
.pipe-stage small { display: block; font-weight: 500; color: var(--text-3); font-size: 11.5px; margin-top: 2px; }
.pipe-stage.prog { border-color: color-mix(in srgb, var(--accent) 50%, var(--border)); }
.pipe-stage.prog::after { content: 'you write this'; position: absolute; top: -9px; left: 50%; transform: translateX(-50%); padding: 0 6px; font-size: 9.5px; font-weight: 700; letter-spacing: .04em; text-transform: uppercase; color: var(--accent); background: var(--surface); border-radius: 4px; white-space: nowrap; }
.pipe-stage:hover { transform: translateY(-2px); box-shadow: var(--shadow); }
.pipe-stage.on { background: var(--accent); color: #fff; border-color: var(--accent); transform: translateY(-3px) scale(1.03); box-shadow: 0 10px 24px -10px var(--accent); }
.pipe-stage.on small { color: rgba(255, 255, 255, .8); }
.pipe-detail { margin-top: 14px; padding: 14px 16px; border-radius: 12px; background: var(--surface-2); border: 1px solid var(--border); min-height: 96px; font-size: 14.5px; }
.pipe-detail h5 { margin: 0 0 4px; font-size: 15px; }

/* ==========================================================================
   Quiz
   ========================================================================== */
.quiz { margin: 48px 0 24px; padding: 22px; border-radius: 18px; border: 1px solid var(--border); background: var(--surface); box-shadow: var(--shadow); }
.quiz-head { display: flex; align-items: center; gap: 10px; margin-bottom: 14px; }
.quiz-head h3 { margin: 0 !important; font-size: 19px !important; }
.quiz-score { margin-left: auto; font-size: 13px; font-weight: 600; color: var(--text-3); }
.q { padding: 16px 0; border-top: 1px solid var(--border); }
.q-text { font-weight: 600; margin-bottom: 10px; }
.q-opts { display: grid; gap: 8px; }
.q-opt {
  text-align: left; padding: 10px 14px; border-radius: 10px; border: 1.5px solid var(--border);
  background: var(--surface-2); cursor: pointer; font-size: 14.5px; line-height: 1.45; transition: all .2s var(--ease);
}
.q-opt:hover:not(:disabled) { border-color: var(--accent); transform: translateX(3px); }
.q-opt.right { border-color: var(--ok); background: var(--ok-soft); }
.q-opt.wrong { border-color: var(--vk); background: var(--vk-soft); animation: shake .4s; }
.q-opt:disabled { cursor: default; }
@keyframes shake { 20%, 60% { transform: translateX(-4px); } 40%, 80% { transform: translateX(4px); } }
.q-explain { margin-top: 10px; padding: 10px 14px; border-radius: 10px; font-size: 14px; background: var(--accent-soft); color: var(--text); animation: pageIn .35s var(--ease); }

/* ==========================================================================
   Lesson footer
   ========================================================================== */
.complete-box { margin: 40px 0 0; padding: 20px 22px; border-radius: 16px; display: flex; align-items: center; gap: 16px; background: var(--surface-2); border: 1px dashed var(--border-strong); }
.complete-box p { margin: 0; flex: 1; font-size: 14.5px; color: var(--text-2); }
.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin-top: 28px; }
.pager a {
  display: block; padding: 16px 18px; border-radius: 14px; border: 1px solid var(--border); background: var(--surface);
  color: var(--text); transition: all .2s var(--ease);
}
.pager a:hover { border-color: var(--accent); text-decoration: none; transform: translateY(-2px); box-shadow: var(--shadow); }
.pager small { display: block; font-size: 12px; color: var(--text-3); font-weight: 600; text-transform: uppercase; letter-spacing: .06em; }
.pager span { font-weight: 650; }
.pager .next { text-align: right; grid-column: 2; }

/* ==========================================================================
   Home page
   ========================================================================== */
.home { max-width: 1120px; margin: 0 auto; }
.hero {
  position: relative; display: grid; grid-template-columns: 1.1fr .9fr; gap: 40px; align-items: center;
  padding: 30px 0 50px;
}
.hero h1 { font-size: clamp(38px, 6vw, 64px); line-height: 1.02; letter-spacing: -.045em; font-weight: 850; margin: 16px 0 18px; }
.hero h1 .grad { background: linear-gradient(100deg, var(--gl) 0%, var(--accent-2) 45%, var(--vk) 100%); -webkit-background-clip: text; background-clip: text; color: transparent; }
.hero p { font-size: 19px; color: var(--text-2); margin: 0 0 26px; max-width: 540px; }
.hero-cta { display: flex; flex-wrap: wrap; gap: 12px; }
.hero-cta .btn { padding: 12px 20px; font-size: 15px; }
.hero-visual { position: relative; aspect-ratio: 1; border-radius: 28px; overflow: hidden; box-shadow: var(--shadow-lg); border: 1px solid var(--border); background: radial-gradient(circle at 30% 20%, #2a1650, #0b0913 70%); }
.hero-visual canvas { width: 100%; height: 100%; }
.hero-visual .hv-tag { position: absolute; bottom: 14px; left: 14px; right: 14px; display: flex; justify-content: space-between; font: 600 11.5px var(--mono); color: rgba(255, 255, 255, .7); pointer-events: none; }
.hero-glow { position: absolute; inset: -20% -10% auto auto; width: 60%; height: 120%; background: radial-gradient(circle, color-mix(in srgb, var(--accent) 25%, transparent), transparent 60%); filter: blur(40px); z-index: -1; pointer-events: none; }

.feature-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 14px; margin: 10px 0 60px; }
.feature { padding: 20px; border-radius: 16px; background: var(--surface); border: 1px solid var(--border); transition: transform .3s var(--ease), box-shadow .3s; }
.feature:hover { transform: translateY(-4px); box-shadow: var(--shadow); }
.feature .f-icon { width: 40px; height: 40px; border-radius: 11px; display: grid; place-items: center; font-size: 20px; margin-bottom: 12px; background: var(--accent-soft); }
.feature h3 { margin: 0 0 6px; font-size: 16px; }
.feature p { margin: 0; font-size: 14px; color: var(--text-2); line-height: 1.55; }

.section-title { display: flex; align-items: end; justify-content: space-between; gap: 20px; margin: 0 0 18px; }
.section-title h2 { margin: 0; font-size: 30px; letter-spacing: -.03em; }
.section-title p { margin: 0; color: var(--text-3); font-size: 15px; }

.roadmap { display: grid; gap: 26px; margin-bottom: 60px; }
.road-group h3 { display: flex; align-items: center; gap: 10px; font-size: 14px; letter-spacing: .08em; text-transform: uppercase; color: var(--text-3); margin: 0 0 12px; }
.road-group h3::after { content: ''; flex: 1; height: 1px; background: var(--border); }
.road-cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 12px; }
.road-card {
  position: relative; display: flex; flex-direction: column; gap: 6px;
  padding: 16px 16px 14px; border-radius: 14px; background: var(--surface); border: 1px solid var(--border);
  color: var(--text); transition: all .25s var(--ease); overflow: hidden;
}
.road-card::before { content: ''; position: absolute; inset: 0 0 auto; height: 3px; background: linear-gradient(90deg, var(--gl), var(--accent-2), var(--vk)); transform: scaleX(0); transform-origin: left; transition: transform .4s var(--ease); }
.road-card:hover { text-decoration: none; border-color: var(--border-strong); transform: translateY(-3px); box-shadow: var(--shadow); }
.road-card:hover::before { transform: scaleX(1); }
.road-card .rc-top { display: flex; align-items: center; gap: 8px; font-size: 12px; font-weight: 700; color: var(--text-3); }
.road-card .rc-top .done-badge { margin-left: auto; color: var(--ok); }
.road-card h4 { margin: 0; font-size: 16px; letter-spacing: -.01em; }
.road-card p { margin: 0; font-size: 13.5px; color: var(--text-2); line-height: 1.5; }
.road-card .rc-tags { display: flex; gap: 6px; margin-top: 4px; flex-wrap: wrap; }
.road-card .rc-tags span { font-size: 11px; font-weight: 600; padding: 2px 8px; border-radius: 99px; background: var(--surface-2); color: var(--text-3); }

.split-explainer { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin-bottom: 60px; }
.split-explainer > div { padding: 24px; border-radius: 18px; border: 1px solid var(--border); background: var(--surface); }
.split-explainer .gl-card { background: linear-gradient(160deg, var(--gl-soft), var(--surface) 60%); }
.split-explainer .vk-card { background: linear-gradient(160deg, var(--vk-soft), var(--surface) 60%); }
.split-explainer h3 { margin: 0 0 8px; font-size: 20px; }
.split-explainer p { margin: 0 0 10px; color: var(--text-2); font-size: 15px; }
.split-explainer ul { margin: 0; padding-left: 18px; color: var(--text-2); font-size: 14.5px; }

.site-foot { margin: 40px auto 0; max-width: 1120px; padding: 24px 0 10px; border-top: 1px solid var(--border); font-size: 13px; color: var(--text-3); display: flex; flex-wrap: wrap; gap: 10px 24px; justify-content: space-between; }

/* Glossary & cheat sheet */
.gloss-search { width: 100%; padding: 12px 16px; border-radius: 12px; border: 1px solid var(--border); background: var(--surface); color: var(--text); font: inherit; margin-bottom: 20px; outline: none; transition: box-shadow .2s, border-color .2s; }
.gloss-search:focus { border-color: var(--accent); box-shadow: 0 0 0 4px var(--accent-soft); }
.gloss-list { display: grid; gap: 10px; }
.gloss-item { padding: 14px 18px; border-radius: 12px; background: var(--surface); border: 1px solid var(--border); }
.gloss-item h4 { margin: 0 0 4px; font-size: 16px; display: flex; gap: 8px; align-items: center; }
.gloss-item p { margin: 0; color: var(--text-2); font-size: 14.5px; }

/* ==========================================================================
   Command palette & toast
   ========================================================================== */
.palette { position: fixed; inset: 0; z-index: 90; display: grid; place-items: start center; padding-top: 12vh; background: rgba(8, 5, 20, .45); backdrop-filter: blur(4px); animation: fadeIn .15s; }
@keyframes fadeIn { from { opacity: 0; } }
.palette-box { width: min(620px, calc(100vw - 32px)); border-radius: 16px; background: var(--surface); border: 1px solid var(--border-strong); box-shadow: var(--shadow-lg); overflow: hidden; animation: popIn .22s var(--ease); }
@keyframes popIn { from { opacity: 0; transform: translateY(-10px) scale(.98); } }
.palette-input { display: flex; align-items: center; gap: 10px; padding: 14px 16px; border-bottom: 1px solid var(--border); color: var(--text-3); }
.palette-input input { flex: 1; border: 0; outline: none; background: none; font: 16px var(--font); color: var(--text); }
#palette-results { list-style: none; margin: 0; padding: 6px; max-height: 50vh; overflow-y: auto; }
#palette-results li a { display: flex; flex-direction: column; padding: 10px 12px; border-radius: 10px; color: var(--text); }
#palette-results li a small { color: var(--text-3); font-size: 12.5px; }
#palette-results li.sel a, #palette-results li a:hover { background: var(--accent-soft); text-decoration: none; }
#palette-results .empty { padding: 20px; text-align: center; color: var(--text-3); font-size: 14px; }
.toast { position: fixed; bottom: 24px; left: 50%; transform: translateX(-50%); z-index: 95; padding: 10px 18px; border-radius: 99px; background: var(--text); color: var(--bg); font-size: 14px; font-weight: 600; box-shadow: var(--shadow-lg); animation: toastIn .3s var(--ease); }
@keyframes toastIn { from { opacity: 0; transform: translate(-50%, 10px); } }

/* ==========================================================================
   Responsive
   ========================================================================== */
@media (max-width: 1280px) {
  .layout { grid-template-columns: var(--sidebar-w) minmax(0, 1fr); }
  .toc { display: none; }
}
@media (max-width: 980px) {
  .hero { grid-template-columns: 1fr; }
  .hero-visual { max-width: 460px; width: 100%; }
  .feature-grid { grid-template-columns: repeat(2, 1fr); }
  .demo-body { grid-template-columns: 1fr; }
  .demo-controls { border-left: 0; border-top: 1px solid var(--border); max-height: none; display: grid; grid-template-columns: repeat(auto-fill, minmax(190px, 1fr)); }
}
@media (max-width: 860px) {
  .only-mobile { display: grid; }
  .layout, .layout.no-toc { grid-template-columns: minmax(0, 1fr); }
  .sidebar {
    position: fixed; top: var(--topbar-h); left: 0; bottom: 0; z-index: 45; height: auto;
    width: min(300px, 86vw); transform: translateX(-102%); transition: transform .3s var(--ease);
    box-shadow: var(--shadow-lg);
  }
  .sidebar.open { transform: none; }
  .scrim { display: block; position: fixed; inset: var(--topbar-h) 0 0; z-index: 44; background: rgba(8, 5, 20, .4); opacity: 0; pointer-events: none; transition: opacity .3s; }
  .scrim.show { opacity: 1; pointer-events: auto; }
  .search-trigger { min-width: 0; margin-left: auto; }
  .search-trigger span, .search-trigger kbd { display: none; }
  .top-links { display: none; }
  .brand-text { display: none; }
  .content { padding: 26px 16px 60px; }
  .compare, .steps-vs, .split-explainer { grid-template-columns: 1fr; }
  .steps-vs .col + .col { margin-top: 12px; }
  .topbar { padding: 0 12px; gap: 10px; }
}
@media (max-width: 540px) {
  .feature-grid { grid-template-columns: 1fr; }
  .pager { grid-template-columns: 1fr; }
  .pager .next { grid-column: 1; }
  .complete-box { flex-direction: column; align-items: stretch; }
  .code pre { font-size: 12.5px; padding: 14px; }
  .section-title { flex-direction: column; align-items: start; gap: 4px; }
}

/* ==========================================================================
   Inline Vulkan 1.4 track (secondary to OpenGL, but woven through each lesson)
   ========================================================================== */
.vk-inline {
  position: relative; margin: 18px 0 26px 0; padding: 12px 16px 14px 18px;
  border-radius: 12px; font-size: 14.5px; line-height: 1.65;
  background: linear-gradient(100deg, color-mix(in srgb, var(--vk) 7%, var(--surface)), var(--surface) 70%);
  border: 1px solid color-mix(in srgb, var(--vk) 22%, var(--border));
  border-left: 3px solid var(--vk);
}
.vk-inline-head { display: flex; align-items: center; gap: 10px; margin-bottom: 6px; }
.vk-pill {
  flex: none; padding: 2px 9px; border-radius: 99px; font: 700 10.5px var(--font); letter-spacing: .06em; text-transform: uppercase;
  color: #fff; background: var(--vk);
}
.vk-inline-title { font-weight: 650; font-size: 14.5px; color: var(--text); }
.vk-inline-body > :last-child { margin-bottom: 0; }
.vk-inline-body p { margin: 0 0 10px; }
.vk-inline .code { margin: 12px 0 10px; }
.vk-inline .compare, .vk-inline .steps-vs { margin: 10px 0; }
.vk-inline table { font-size: 13.5px; }
.code-tab.vk-tab { color: color-mix(in srgb, var(--vk) 75%, var(--text-3)); }
.code-tab.vk-tab.active::after { background: var(--vk); }
body.no-vk .vk-inline, body.no-vk .vk-tab, body.no-vk .vk-track { display: none !important; }

.tracks { display: grid; grid-template-columns: 1.35fr 1fr; gap: 10px; margin: -14px 0 34px; }
.track { padding: 12px 14px; border-radius: 12px; font-size: 13.5px; line-height: 1.5; color: var(--text-2); border: 1px solid var(--border); background: var(--surface); }
.track b { display: block; font-size: 11px; letter-spacing: .08em; text-transform: uppercase; margin-bottom: 3px; }
.track.gl-track { border-color: color-mix(in srgb, var(--gl) 35%, var(--border)); background: linear-gradient(120deg, var(--gl-soft), var(--surface) 70%); }
.track.gl-track b { color: var(--gl); }
.track.vk-track b { color: var(--vk); }
@media (max-width: 700px) { .tracks { grid-template-columns: 1fr; } }

/* ==========================================================================
   Sandbox
   ========================================================================== */
.sandbox-page { max-width: 1400px; margin: 0 auto; }
.sb-head { display: flex; flex-wrap: wrap; align-items: center; gap: 10px 14px; margin-bottom: 14px; }
.sb-head h1 { font-size: 28px; letter-spacing: -.03em; margin: 0; font-weight: 800; }
.sb-head .sb-actions { margin-left: auto; display: flex; flex-wrap: wrap; gap: 8px; }
.sb-head select { font: 600 13px var(--font); padding: 8px 10px; border-radius: 10px; border: 1px solid var(--border); background: var(--surface); color: var(--text); }
.sb-grid { display: grid; grid-template-columns: minmax(0, 1.05fr) minmax(0, 1fr); gap: 14px; height: calc(100vh - var(--topbar-h) - 150px); min-height: 560px; }
.sb-pane { display: flex; flex-direction: column; min-height: 0; border-radius: 16px; border: 1px solid var(--border); background: var(--surface); overflow: hidden; box-shadow: var(--shadow); }
.sb-pane-head { display: flex; align-items: center; gap: 8px; padding: 8px 12px; border-bottom: 1px solid var(--border); background: var(--surface-2); font: 600 12.5px var(--font); color: var(--text-2); }
.sb-pane-head .sp { margin-left: auto; font-weight: 500; color: var(--text-3); }
.sb-editor { position: relative; flex: 1; min-height: 0; background: var(--code-bg); }
.sb-editor pre, .sb-editor textarea {
  position: absolute; inset: 0; margin: 0; padding: 14px 16px 14px 56px; border: 0; overflow: auto;
  font: 13px/1.6 var(--mono); tab-size: 4; white-space: pre; word-wrap: normal;
}
.sb-editor pre { pointer-events: none; color: var(--code-text); }
.sb-editor textarea { resize: none; outline: none; background: transparent; color: transparent; caret-color: var(--text); }
.sb-editor textarea::selection { background: color-mix(in srgb, var(--accent) 35%, transparent); color: transparent; }
.sb-gutter { position: absolute; top: 0; left: 0; width: 44px; white-space: pre; padding: 14px 8px 14px 0; text-align: right; font: 13px/1.6 var(--mono); color: var(--tok-com); opacity: .6; pointer-events: none; overflow: hidden; height: 100%; }
.sb-gutter .err { color: var(--vk); opacity: 1; font-weight: 700; }
.sb-right { display: grid; grid-template-rows: minmax(0, 1.4fr) minmax(0, 1fr); gap: 14px; min-height: 0; }
.sb-stage { position: relative; flex: 1; background: #0b0913; min-height: 0; }
.sb-stage canvas { position: absolute; inset: 0; width: 100%; height: 100%; outline: none; }
.sb-stage .sb-idle { position: absolute; inset: 0; display: grid; place-items: center; color: #847c9f; font-size: 14px; text-align: center; padding: 20px; }
.sb-console { flex: 1; min-height: 0; overflow: auto; padding: 10px 14px; font: 12.5px/1.55 var(--mono); background: var(--code-bg); color: var(--code-text); white-space: pre-wrap; }
.sb-console .err { color: var(--vk); }
.sb-console .info { color: var(--text-3); }
.sb-console .ok { color: var(--ok); }
.sb-status { display: inline-flex; align-items: center; gap: 6px; }
.sb-status::before { content: ''; width: 8px; height: 8px; border-radius: 50%; background: var(--text-3); }
.sb-status.running::before { background: var(--ok); animation: pulse 2s infinite; }
.sb-status.error::before { background: var(--vk); }
.sb-libs { display: flex; flex-wrap: wrap; gap: 6px; margin: 0 0 14px; }
@media (max-width: 1000px) { .sb-grid { grid-template-columns: 1fr; height: auto; } .sb-pane.code-pane { height: 60vh; } .sb-right { grid-template-rows: 380px 260px; } }

/* Sandbox route */
.sb-frame { display: block; width: 100%; height: calc(100vh - var(--topbar-h) - 170px); min-height: 640px; border: 1px solid var(--border); border-radius: 16px; background: var(--bg); box-shadow: var(--shadow); }
.sb-note { margin: 12px 2px 0; font-size: 13.5px; color: var(--text-3); }
.sb-note code { font: 500 .9em var(--mono); }
.sb-try .btn { margin-top: 2px; }
@media (max-width: 900px) { .sb-frame { height: 1200px; } }

/* ==========================================================================
   Wide code: prose stays in a readable column, code / demos / tables break out wider
   ========================================================================== */
.article {
  max-width: none;
  display: grid;
  grid-template-columns: minmax(0, 1fr) min(760px, 100%) minmax(0, 1fr);
}
.article > * { grid-column: 2; min-width: 0; }
.article > .code,
.article > .demo,
.article > .table-scroll,
.article > .vk-inline:has(.code),
.article > .quiz { grid-column: 1 / -1; justify-self: center; width: 100%; max-width: 1240px; }
.article > .quiz { max-width: 760px; }
.article > .vk-inline:has(.code) .vk-inline-body > p,
.article > .vk-inline:has(.code) .vk-inline-body > ul { max-width: 760px; }
.code pre { font-size: 13px; }
.code pre.wrap { white-space: pre-wrap; word-break: break-word; }
.code pre.wrap .hl-line { width: auto; }

/* ==========================================================================
   Collapsible sidebar (desktop) — toggled from the top bar or with the [ key
   ========================================================================== */
.layout { transition: grid-template-columns .3s var(--ease); }
.sidebar { transition: opacity .2s; }
@media (min-width: 861px) {
  body.sidebar-collapsed .layout { grid-template-columns: 0 minmax(0, 1fr) var(--toc-w); }
  body.sidebar-collapsed .layout.no-toc { grid-template-columns: 0 minmax(0, 1fr); }
  body.sidebar-collapsed .sidebar { opacity: 0; pointer-events: none; overflow: hidden; padding: 0; border: 0; }
  .only-mobile { display: grid; }   /* the menu button doubles as the sidebar toggle on desktop */
}
/* The right-hand table of contents only appears when there's room left for wide code. */
@media (min-width: 861px) and (max-width: 1680px) {
  .layout { grid-template-columns: var(--sidebar-w) minmax(0, 1fr); }
  .toc { display: none; }
  body.sidebar-collapsed .layout { grid-template-columns: 0 minmax(0, 1fr); }
}

/* ==========================================================================
   Sandbox route: full screen, no sidebar
   ========================================================================== */
body.route-sandbox { overflow: hidden; }
body.route-sandbox .sidebar, body.route-sandbox .toc, body.route-sandbox .progress-bar, body.route-sandbox .scrim { display: none !important; }
body.route-sandbox .layout, body.route-sandbox .layout.no-toc { grid-template-columns: minmax(0, 1fr) !important; }
body.route-sandbox .content { padding: 0; }
body.route-sandbox #menu-btn { display: none !important; }
body.route-sandbox .sandbox-page { max-width: none; }
body.route-sandbox .sb-frame { height: calc(100vh - var(--topbar-h)); min-height: 0; border: 0; border-radius: 0; box-shadow: none; }
body.route-sandbox .sb-file { max-width: 640px; margin: 40px auto; padding: 0 16px; }

/* Syntax colours for the sandbox editor (same palette as the lesson code blocks). */
.sb-editor .tok-kw { color: var(--tok-kw); font-weight: 600; }
.sb-editor .tok-type { color: var(--tok-type); }
.sb-editor .tok-str { color: var(--tok-str); }
.sb-editor .tok-num { color: var(--tok-num); }
.sb-editor .tok-com { color: var(--tok-com); font-style: italic; }
.sb-editor .tok-fn { color: var(--tok-fn); }
.sb-editor .tok-pre { color: var(--tok-pre); }