:root {
  --bg: #0d1117;
  --bg-secondary: #161b22;
  --text: #e6edf3;
  --text-muted: #7d8590;
  --grid: #21262d;
  --border: #30363d;
  --blue: #58a6ff;
  --green: #3fb950;
  --orange: #f78166;
  --purple: #d2a8ff;
  --gold: #f0e68c;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  font-size: 18px;
  line-height: 1.7;
}

.page {
  max-width: 720px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
}

h1, h2, h3, h4 {
  line-height: 1.3;
  margin-top: 2.5rem;
  margin-bottom: 1rem;
}

h1 { font-size: 2.2rem; }
h2 { font-size: 1.6rem; color: var(--blue); }
h3 { font-size: 1.3rem; }

p { margin-bottom: 1.2rem; }

a { color: var(--blue); text-decoration: none; }
a:hover { text-decoration: underline; }

/* KaTeX overrides */
.katex { color: var(--text); }
.katex-display { margin: 2rem 0; overflow-x: auto; }

/* Code blocks */
code {
  background: var(--bg-secondary);
  padding: 0.15em 0.4em;
  border-radius: 4px;
  font-size: 0.9em;
}

pre {
  background: var(--bg-secondary);
  padding: 1.2rem;
  border-radius: 8px;
  overflow-x: auto;
  margin-bottom: 1.5rem;
}

pre code { background: none; padding: 0; }

/* SVG diagrams */
.diagram {
  max-width: 900px;
  margin: 2rem auto;
  text-align: center;
}

.diagram svg {
  width: 100%;
  height: auto;
}

/* SVG color classes */
svg .grid-line { stroke: var(--grid); stroke-width: 1; }
svg .axis { stroke: var(--text-muted); stroke-width: 1.5; }
svg .vec-primary { stroke: var(--blue); stroke-width: 2.5; fill: none; }
svg .vec-secondary { stroke: var(--green); stroke-width: 2.5; fill: none; }
svg .vec-result { stroke: var(--orange); stroke-width: 2.5; fill: none; }
svg .vec-eigen { stroke: var(--purple); stroke-width: 2.5; fill: none; }
svg .vec-highlight { stroke: var(--gold); stroke-width: 2.5; fill: none; }
svg .label { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif; font-size: 14px; }
svg .label-primary { fill: var(--blue); }
svg .label-secondary { fill: var(--green); }
svg .label-result { fill: var(--orange); }
svg .label-muted { fill: var(--text-muted); }
svg .area-fill { opacity: 0.15; }
svg .dashed { stroke-dasharray: 6,4; }
svg .origin { fill: var(--text-muted); }
/* Marker polygons use explicit fill="var(--color)" attributes */

/* Callout / Key Takeaway */
.callout {
  background: var(--bg-secondary);
  border-left: 4px solid var(--gold);
  padding: 1.2rem 1.5rem;
  margin: 2rem 0;
  border-radius: 0 8px 8px 0;
}

.callout p { margin-bottom: 0; }

/* Chapter navigation */
.chapter-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
}

.chapter-nav a {
  color: var(--text-muted);
  font-size: 0.95rem;
}

.chapter-nav a:hover { color: var(--blue); }

/* Table of contents */
.toc { list-style: none; }

.toc li { margin-bottom: 0.5rem; }

.toc .part-title {
  color: var(--text-muted);
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-top: 1.5rem;
  margin-bottom: 0.5rem;
}

strong { color: var(--text); }
em { color: var(--text-muted); font-style: italic; }

/* Chapter header */
.chapter-number {
  color: var(--text-muted);
  font-size: 0.9rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.25rem;
}

/* Site header */
.site-header {
  text-align: center;
  margin-bottom: 3rem;
  padding-bottom: 2rem;
  border-bottom: 1px solid var(--border);
}

.subtitle {
  color: var(--text-muted);
  font-size: 1.1rem;
  margin-top: 0.5rem;
}

.chapter-num {
  color: var(--text-muted);
  display: inline-block;
  width: 2rem;
}

/* ===== Chapter Sidebar ===== */

.chapter-sidebar-toggle {
  position: fixed;
  top: 1rem;
  left: 1rem;
  z-index: 100;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  color: var(--text-muted);
  width: 36px;
  height: 36px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: color 0.15s, border-color 0.15s;
}

.chapter-sidebar-toggle:hover {
  color: var(--text);
  border-color: var(--text-muted);
}

.chapter-sidebar {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 200;
  width: 300px;
  height: 100vh;
  background: var(--bg-secondary);
  border-right: 1px solid var(--border);
  transform: translateX(-100%);
  transition: transform 0.25s ease;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.chapter-sidebar.open {
  transform: translateX(0);
}

.chapter-sidebar-overlay {
  position: fixed;
  inset: 0;
  z-index: 150;
  background: rgba(0, 0, 0, 0.5);
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.25s ease;
}

.chapter-sidebar-overlay.open {
  opacity: 1;
  pointer-events: auto;
}

.chapter-sidebar-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}

.chapter-sidebar-home {
  font-weight: 600;
  font-size: 1rem;
  color: var(--text);
}

.chapter-sidebar-close {
  background: none;
  border: 1px solid var(--border);
  color: var(--text-muted);
  width: 28px;
  height: 28px;
  border-radius: 4px;
  cursor: pointer;
  font-size: 1.2rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.chapter-sidebar-close:hover {
  color: var(--text);
  border-color: var(--text-muted);
}

.chapter-sidebar-content {
  flex: 1;
  overflow-y: auto;
  padding: 0.75rem 0;
}

.chapter-sidebar-part {
  margin-bottom: 0.5rem;
}

.chapter-sidebar-part-title {
  color: var(--text-muted);
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 0.5rem 1rem 0.25rem;
}

.chapter-sidebar-link {
  display: flex;
  align-items: baseline;
  gap: 0.4rem;
  padding: 0.35rem 1rem;
  font-size: 0.85rem;
  color: var(--text);
  text-decoration: none;
  transition: background 0.1s;
}

.chapter-sidebar-link:hover {
  background: var(--bg);
  text-decoration: none;
}

.chapter-sidebar-link.active {
  color: var(--blue);
  background: var(--bg);
}

.chapter-sidebar-num {
  color: var(--text-muted);
  min-width: 1.5rem;
  flex-shrink: 0;
}

.chapter-sidebar-link.active .chapter-sidebar-num {
  color: var(--blue);
}

@media (max-width: 600px) {
  .chapter-sidebar {
    width: 85%;
  }
}

/* ===== Playground ===== */

.playground-container {
  display: flex;
  height: 100vh;
  overflow: hidden;
}

.page:has(> .playground-container) {
  max-width: none;
  padding: 0;
  height: 100vh;
  overflow: hidden;
}

.playground-sidebar {
  width: 320px;
  min-width: 280px;
  background: var(--bg-secondary);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  flex-shrink: 0;
  transition: width 0.2s, min-width 0.2s;
}

.playground-sidebar.collapsed {
  width: 0;
  min-width: 0;
  overflow: hidden;
  border-right: none;
}

.sidebar-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--border);
}

.back-link {
  color: var(--text-muted);
  font-size: 0.85rem;
}

.sidebar-toggle {
  background: none;
  border: 1px solid var(--border);
  color: var(--text-muted);
  width: 28px;
  height: 28px;
  border-radius: 4px;
  cursor: pointer;
  font-size: 1rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.sidebar-toggle:hover {
  color: var(--text);
  border-color: var(--text-muted);
}

.sidebar-content {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.example-browser {
  flex: 1;
  overflow-y: auto;
  padding: 0.75rem 1rem;
  min-height: 150px;
}

.example-browser h3,
.code-editor-panel h3 {
  font-size: 0.85rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin: 0 0 0.75rem 0;
}

.example-search {
  width: 100%;
  padding: 0.4rem 0.6rem;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 4px;
  color: var(--text);
  font-size: 0.85rem;
  margin-bottom: 0.75rem;
  outline: none;
}

.example-search:focus {
  border-color: var(--blue);
}

.example-list {
  font-size: 0.85rem;
}

.example-chapter {
  margin-bottom: 0.5rem;
}

.example-chapter-header {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.3rem 0;
  color: var(--text-muted);
  cursor: pointer;
  font-size: 0.8rem;
  user-select: none;
}

.example-chapter-header:hover {
  color: var(--text);
}

.example-chapter-header .arrow {
  font-size: 0.65rem;
  transition: transform 0.15s;
}

.example-chapter.collapsed .arrow {
  transform: rotate(-90deg);
}

.example-chapter.collapsed .example-chapter-items {
  display: none;
}

.example-item {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.35rem 0.5rem;
  margin-left: 0.75rem;
  border-radius: 4px;
  cursor: pointer;
  color: var(--text);
}

.example-item:hover {
  background: var(--bg);
}

.example-item.active {
  background: var(--bg);
  color: var(--blue);
}

.example-item .name {
  flex: 1;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.example-tag {
  font-size: 0.65rem;
  padding: 0.1rem 0.35rem;
  border-radius: 3px;
  border: 1px solid var(--border);
  color: var(--text-muted);
  cursor: pointer;
  white-space: nowrap;
}

.example-tag:hover {
  border-color: var(--blue);
  color: var(--blue);
}

.example-tag.tag-2d { border-color: var(--green); color: var(--green); }
.example-tag.tag-3d { border-color: var(--purple); color: var(--purple); }

.sidebar-divider {
  height: 4px;
  background: var(--border);
  cursor: row-resize;
  flex-shrink: 0;
}

.sidebar-divider:hover {
  background: var(--blue);
}

.code-editor-panel {
  flex: 1;
  display: flex;
  flex-direction: column;
  padding: 0.75rem 1rem;
  min-height: 200px;
  overflow: hidden;
}

.code-editor {
  flex: 1;
  width: 100%;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text);
  font-family: "SF Mono", "Fira Code", "Cascadia Code", monospace;
  font-size: 0.8rem;
  line-height: 1.5;
  padding: 0.75rem;
  resize: none;
  outline: none;
  tab-size: 2;
}

.code-editor:focus {
  border-color: var(--blue);
}

.editor-controls {
  display: flex;
  gap: 0.5rem;
  margin-top: 0.5rem;
}

.btn {
  background: var(--bg);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 0.4rem 0.8rem;
  border-radius: 4px;
  cursor: pointer;
  font-size: 0.8rem;
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
}

.btn:hover {
  border-color: var(--text-muted);
}

.btn-run {
  background: var(--blue);
  border-color: var(--blue);
  color: var(--bg);
  font-weight: 600;
}

.btn-run:hover {
  opacity: 0.9;
  border-color: var(--blue);
}

.btn kbd {
  font-size: 0.7rem;
  opacity: 0.7;
}

.btn-sm {
  padding: 0.25rem 0.5rem;
  font-size: 0.75rem;
}

.btn-sm.active {
  background: var(--blue);
  border-color: var(--blue);
  color: var(--bg);
}

.error-output {
  color: var(--orange);
  font-family: "SF Mono", "Fira Code", monospace;
  font-size: 0.75rem;
  margin-top: 0.5rem;
  max-height: 4rem;
  overflow-y: auto;
  white-space: pre-wrap;
}

/* Canvas area */

.playground-canvas-area {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.canvas-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.5rem 1rem;
  border-bottom: 1px solid var(--border);
  background: var(--bg-secondary);
  gap: 1rem;
}

.toolbar-left,
.toolbar-right {
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.toolbar-center {
  font-size: 0.8rem;
  color: var(--text-muted);
}

.speed-control {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.75rem;
  color: var(--text-muted);
}

.speed-control input[type="range"] {
  width: 60px;
  accent-color: var(--blue);
}

.canvas-wrapper {
  flex: 1;
  position: relative;
  overflow: hidden;
}

.canvas-wrapper canvas,
.canvas-wrapper #canvas-3d {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

/* Responsive */
@media (max-width: 768px) {
  .playground-container {
    flex-direction: column;
  }

  .playground-sidebar {
    width: 100%;
    min-width: 100%;
    max-height: 50vh;
    border-right: none;
    border-bottom: 1px solid var(--border);
  }

  .playground-sidebar.collapsed {
    max-height: 0;
    width: 100%;
    min-width: 100%;
  }
}

@media (max-width: 600px) {
  body { font-size: 16px; }
  .page { padding: 1rem; }
  h1 { font-size: 1.8rem; }
  .diagram { max-width: 100%; }
}