/* ============================================
   CSS Custom Properties (Design Tokens)
   ============================================ */
:root {
  /* Color palette - Dark theme (default) */
  --bg-primary: #0d1117;
  --bg-secondary: #161b22;
  --bg-code: #1c2128;
  --text-primary: #c9d1d9;
  --text-secondary: #8b949e;
  --text-heading: #f0f6fc;
  --accent: #58a6ff;
  --accent-hover: #79b8ff;
  --border: #30363d;
  
  /* Syntax highlighting */
  --code-keyword: #ff7b72;
  --code-string: #a5d6ff;
  --code-type: #7ee787;
  --code-comment: #8b949e;
  --code-function: #d2a8ff;
  --code-number: #79c0ff;
  
  /* Spacing scale using fluid values */
  --space-xs: clamp(0.25rem, 0.5vw, 0.5rem);
  --space-sm: clamp(0.5rem, 1vw, 0.75rem);
  --space-md: clamp(1rem, 2vw, 1.5rem);
  --space-lg: clamp(1.5rem, 3vw, 2rem);
  --space-xl: clamp(2rem, 4vw, 3rem);
  
  /* Typography scale using fluid values */
  --font-xs: clamp(0.75rem, 0.7rem + 0.25vw, 0.875rem);
  --font-sm: clamp(0.8125rem, 0.75rem + 0.3vw, 0.9375rem);
  --font-base: clamp(0.875rem, 0.8rem + 0.35vw, 1rem);
  --font-md: clamp(1rem, 0.9rem + 0.5vw, 1.125rem);
  --font-lg: clamp(1.25rem, 1.1rem + 0.75vw, 1.5rem);
  --font-xl: clamp(1.5rem, 1.3rem + 1vw, 2rem);
  
  /* Font families */
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Noto Sans', Helvetica, Arial, sans-serif;
  --font-mono: 'SF Mono', 'Fira Code', 'Consolas', 'Monaco', monospace;
  
  /* Animation */
  --transition-fast: 150ms ease;
  --transition-base: 200ms ease;
  --transition-slow: 300ms ease;
  
  /* Layout */
  --header-height: clamp(56px, 8vh, 72px);
  --nav-height: clamp(44px, 6vh, 56px);
  --content-max-width: 1600px;
  --touch-target-min: 44px;
}

/* Light theme */
[data-theme="light"] {
  --bg-primary: #ffffff;
  --bg-secondary: #f6f8fa;
  --bg-code: #f0f2f4;
  --text-primary: #24292f;
  --text-secondary: #57606a;
  --text-heading: #1f2328;
  --accent: #0969da;
  --accent-hover: #0550ae;
  --border: #d0d7de;
  --code-keyword: #cf222e;
  --code-string: #0a3069;
  --code-type: #116329;
  --code-comment: #6e7781;
  --code-function: #8250df;
  --code-number: #0550ae;
}

/* ============================================
   Base Reset & Global Styles
   ============================================ */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
}

/* Respect user motion preferences */
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

body {
  font-family: var(--font-sans);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
  min-height: 100dvh; /* Dynamic viewport height for mobile */
}

/* ============================================
   Skip Link (Accessibility)
   ============================================ */
.skip-link {
  position: absolute;
  top: -100%;
  left: 50%;
  transform: translateX(-50%);
  padding: var(--space-sm) var(--space-md);
  background: var(--accent);
  color: var(--bg-primary);
  text-decoration: none;
  font-weight: 600;
  border-radius: 0 0 8px 8px;
  z-index: 10000;
  transition: top var(--transition-fast);
}

.skip-link:focus {
  top: 0;
  outline: 3px solid var(--accent-hover);
  outline-offset: 2px;
}

/* ============================================
   Header
   ============================================ */
header {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-md);
  min-height: var(--header-height);
  padding-inline: var(--space-md);
  background: var(--bg-secondary);
  border-block-end: 1px solid var(--border);
}

header h1 {
  color: var(--text-heading);
  font-size: var(--font-lg);
  font-weight: 600;
}

header h1 span {
  color: var(--accent);
}

.header-controls {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

/* ============================================
   Theme Toggle Button
   ============================================ */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: var(--touch-target-min);
  min-height: var(--touch-target-min);
  padding: var(--space-sm);
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text-secondary);
  cursor: pointer;
  transition: color var(--transition-fast), 
              border-color var(--transition-fast),
              background var(--transition-fast);
}

.theme-toggle:hover {
  color: var(--accent);
  border-color: var(--accent);
}

.theme-toggle:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.theme-toggle svg {
  width: 20px;
  height: 20px;
  flex-shrink: 0;
}

.theme-toggle .sun-icon { display: none; }
.theme-toggle .moon-icon { display: block; }

[data-theme="light"] .theme-toggle .sun-icon { display: block; }
[data-theme="light"] .theme-toggle .moon-icon { display: none; }

/* ============================================
   GitHub Link
   ============================================ */
.github-link {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: var(--touch-target-min);
  min-height: var(--touch-target-min);
  padding: var(--space-sm);
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text-secondary);
  text-decoration: none;
  transition: color var(--transition-fast), 
              border-color var(--transition-fast),
              background var(--transition-fast);
}

.github-link:hover {
  color: var(--accent);
  border-color: var(--accent);
}

.github-link:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.github-link svg {
  width: 20px;
  height: 20px;
  flex-shrink: 0;
}

/* ============================================
   CSS-Only Mobile Menu
   ============================================ */
.mobile-menu-checkbox {
  position: absolute;
  opacity: 0;
  pointer-events: none;
  /* Position it so the sibling selector works with nav */
}

.mobile-menu-btn {
  display: none;
  align-items: center;
  justify-content: center;
  min-width: var(--touch-target-min);
  min-height: var(--touch-target-min);
  padding: var(--space-sm);
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text-secondary);
  cursor: pointer;
  transition: color var(--transition-fast), border-color var(--transition-fast);
}

.mobile-menu-btn:hover {
  color: var(--accent);
  border-color: var(--accent);
}

.mobile-menu-btn:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.mobile-menu-btn svg {
  width: 20px;
  height: 20px;
  flex-shrink: 0;
}

.mobile-menu-btn .close-icon { display: none; }
.mobile-menu-btn .menu-icon { display: block; }

/* ============================================
   Navigation
   ============================================ */
nav {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm) var(--space-md);
  padding: var(--space-sm) var(--space-md);
  background: var(--bg-secondary);
  border-block-end: 1px solid var(--border);
}

nav a {
  display: inline-flex;
  align-items: center;
  min-height: var(--touch-target-min);
  padding: var(--space-xs) var(--space-sm);
  color: var(--text-secondary);
  font-size: var(--font-sm);
  text-decoration: none;
  border-radius: 6px;
  transition: color var(--transition-fast), background var(--transition-fast);
}

nav a:hover {
  color: var(--accent);
  background: rgba(88, 166, 255, 0.1);
}

nav a:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

nav a.active {
  color: var(--accent);
  background: rgba(88, 166, 255, 0.15);
}

/* ============================================
   Main Content
   ============================================ */
main {
  max-width: var(--content-max-width);
  margin-inline: auto;
  padding: var(--space-lg);
}

/* ============================================
   Sections
   ============================================ */
section {
  margin-block-end: var(--space-xl);
  scroll-margin-block-start: calc(var(--header-height) + var(--nav-height) + var(--space-md));
}

section#overview {
  scroll-margin-block-start: calc(var(--header-height) + var(--space-sm));
}

section h3 {
  color: var(--text-heading);
  font-size: var(--font-md);
  margin-block: var(--space-md) var(--space-sm);
}

/* ============================================
   Collapsible Section Header
   ============================================ */
.section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-sm);
  margin-block-end: var(--space-md);
  padding-block-end: var(--space-sm);
  border-block-end: 1px solid var(--border);
  color: var(--text-heading);
  font-size: var(--font-lg);
  cursor: pointer;
  user-select: none;
  transition: color var(--transition-fast);
}

.section-header:hover {
  color: var(--accent);
}

.section-header span {
  flex: 1;
}

.collapse-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: var(--touch-target-min);
  min-height: var(--touch-target-min);
  padding: var(--space-xs);
  background: transparent;
  border: none;
  color: var(--text-secondary);
  cursor: pointer;
  border-radius: 4px;
  transition: color var(--transition-fast), background var(--transition-fast);
}

.collapse-btn:hover {
  color: var(--accent);
  background: rgba(88, 166, 255, 0.1);
}

.collapse-btn:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.collapse-btn svg {
  width: 20px;
  height: 20px;
  transition: transform var(--transition-slow);
}

/* Section content animation */
.section-content {
  overflow: hidden;
  transition: max-height 0.4s ease, opacity var(--transition-slow);
  max-height: 10000px;
  opacity: 1;
}

/* Collapsed state */
section.collapsed .section-content {
  max-height: 0;
  opacity: 0;
}

section.collapsed .collapse-btn svg {
  transform: rotate(-90deg);
}

section.collapsed .section-header {
  margin-block-end: 0;
  border-block-end-color: transparent;
}

/* ============================================
   Two-Column Documentation Layout
   ============================================ */
.doc-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-md);
  margin-block-end: var(--space-lg);
  align-items: start;
}

/* ============================================
   Documentation Content Column
   ============================================ */
.doc-content {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: var(--space-md);
}

.doc-content h4 {
  color: var(--accent);
  font-size: var(--font-base);
  font-family: var(--font-mono);
  margin-block-end: var(--space-sm);
}

.doc-content p {
  color: var(--text-primary);
  margin-block-end: var(--space-sm);
}

.doc-content ul {
  margin-inline-start: var(--space-md);
  margin-block-end: var(--space-sm);
}

.doc-content li {
  color: var(--text-secondary);
  margin-block-end: var(--space-xs);
}

.doc-content .param {
  background: var(--bg-code);
  padding: var(--space-sm) var(--space-sm);
  border-radius: 6px;
  margin-block-end: var(--space-xs);
}

.doc-content .param-name {
  color: var(--code-function);
  font-family: var(--font-mono);
  font-size: var(--font-sm);
}

.doc-content .param-type {
  color: var(--code-type);
  font-family: var(--font-mono);
  font-size: var(--font-sm);
  margin-inline-start: var(--space-xs);
}

.doc-content .param-desc {
  color: var(--text-secondary);
  font-size: var(--font-sm);
  margin-block-start: var(--space-xs);
}

/* ============================================
   Tags
   ============================================ */
.tag {
  display: inline-block;
  padding: 0.125rem var(--space-sm);
  border-radius: 4px;
  font-size: var(--font-xs);
  font-weight: 500;
  margin-inline-end: var(--space-xs);
  margin-block-end: var(--space-xs);
  text-decoration: none;
  transition: filter var(--transition-fast);
}

a.tag:hover {
  filter: brightness(1.2);
  text-decoration: underline;
}

a.tag:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.tag-protocol { background: rgba(126, 231, 135, 0.15); color: var(--code-type); }
.tag-struct { background: rgba(210, 168, 255, 0.15); color: var(--code-function); }
.tag-enum { background: rgba(255, 123, 114, 0.15); color: var(--code-keyword); }
.tag-mainactor { background: rgba(121, 192, 255, 0.15); color: var(--code-number); }
.tag-throws { background: rgba(255, 166, 87, 0.15); color: #ffa657; }
.tag-sendable { background: rgba(126, 231, 135, 0.15); color: var(--code-type); }

/* ============================================
   Code Content Column
   ============================================ */
.code-content {
  position: relative;
  background: var(--bg-code);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
  /* Container query context for responsive code blocks */
  container-type: inline-size;
  container-name: code-block;
}

.code-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-sm);
  background: var(--bg-secondary);
  border-block-end: 1px solid var(--border);
}

.code-header .filename {
  color: var(--text-secondary);
  font-family: var(--font-mono);
  font-size: var(--font-xs);
}

.code-header .lines {
  color: var(--text-secondary);
  font-size: var(--font-xs);
}

pre {
  padding: var(--space-sm);
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: var(--font-xs);
  line-height: 1.5;
  -webkit-overflow-scrolling: touch; /* Smooth scrolling on iOS */
}

code {
  font-family: inherit;
}

/* Container query for code blocks on smaller containers */
@container code-block (max-width: 400px) {
  pre {
    font-size: 0.7rem;
    padding: var(--space-xs);
  }
  
  .code-header {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.25rem;
  }
}

/* ============================================
   Syntax Highlighting
   ============================================ */
.keyword { color: var(--code-keyword); }
.type { color: var(--code-type); }
.string { color: var(--code-string); }
.comment { color: var(--code-comment); font-style: italic; }
.function { color: var(--code-function); }
.number { color: var(--code-number); }
.property { color: var(--code-number); }

/* Shell/Terminal syntax highlighting */
.shell-prompt { color: var(--code-type); }
.shell-command { color: var(--code-function); }
.shell-flag { color: var(--code-keyword); }
.shell-arg { color: var(--code-string); }
.shell-pipe { color: var(--code-keyword); font-weight: bold; }
.shell-url { color: var(--code-number); text-decoration: underline; }

/* ============================================
   Method Signature Display
   ============================================ */
.signature {
  background: var(--bg-code);
  padding: var(--space-sm) var(--space-sm);
  border-radius: 6px;
  margin-block-end: var(--space-sm);
  font-family: var(--font-mono);
  font-size: var(--font-xs);
  line-height: 1.5;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

/* ============================================
   Intro Section (Overview)
   ============================================ */
.intro {
  background: linear-gradient(135deg, var(--bg-secondary) 0%, var(--bg-code) 100%);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: var(--space-lg);
  margin-block-end: var(--space-lg);
}

.intro h2 {
  border: none;
  padding: 0;
  margin-block-end: var(--space-sm);
}

.intro p {
  color: var(--text-secondary);
  font-size: var(--font-md);
}

.features {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(200px, 100%), 1fr));
  gap: var(--space-sm);
  margin-block-start: var(--space-md);
}

.feature {
  background: var(--bg-primary);
  padding: var(--space-sm);
  border-radius: 8px;
  border: 1px solid var(--border);
}

.feature h4 {
  color: var(--accent);
  font-size: var(--font-sm);
  margin-block-end: var(--space-xs);
}

.feature p {
  color: var(--text-secondary);
  font-size: var(--font-sm);
}

/* ============================================
   Architecture Diagram
   ============================================ */
.architecture {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: var(--space-lg);
  margin-block-end: var(--space-lg);
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.architecture pre {
  background: var(--bg-code);
  border-radius: 6px;
  color: var(--text-primary);
}

.architecture pre.mermaid {
  background: transparent;
  display: flex;
  justify-content: center;
  padding: var(--space-sm) 0;
}

.architecture .mermaid svg {
  max-width: 100%;
  height: auto;
}

/* ============================================
   Mermaid Dark Theme (default)
   ============================================ */
.mermaid .node rect,
.mermaid .node polygon,
.mermaid .node circle,
.mermaid .node ellipse {
  fill: var(--bg-secondary) !important;
  stroke: var(--border) !important;
}

.mermaid .cluster rect {
  fill: var(--bg-code) !important;
  stroke: var(--border) !important;
}

.mermaid .nodeLabel,
.mermaid .cluster-label .nodeLabel,
.mermaid .label {
  color: var(--text-primary) !important;
  fill: var(--text-primary) !important;
}

.mermaid .edgeLabel {
  background-color: var(--bg-secondary) !important;
  color: var(--text-primary) !important;
}

.mermaid .edgeLabel rect {
  fill: var(--bg-secondary) !important;
}

.mermaid .edgeLabel span,
.mermaid .edgeLabel p {
  background-color: var(--bg-secondary) !important;
  color: var(--text-primary) !important;
}

.mermaid .edgePath .path,
.mermaid .flowchart-link {
  stroke: var(--accent) !important;
}

.mermaid .marker,
.mermaid .arrowheadPath {
  fill: var(--accent) !important;
  stroke: var(--accent) !important;
}

/* ============================================
   Mermaid Light Theme
   ============================================ */
[data-theme="light"] .mermaid .node rect,
[data-theme="light"] .mermaid .node polygon,
[data-theme="light"] .mermaid .node circle,
[data-theme="light"] .mermaid .node ellipse {
  fill: #ffffff !important;
  stroke: var(--border) !important;
}

[data-theme="light"] .mermaid .cluster rect {
  fill: var(--bg-secondary) !important;
  stroke: var(--border) !important;
}

[data-theme="light"] .mermaid .nodeLabel,
[data-theme="light"] .mermaid .cluster-label .nodeLabel,
[data-theme="light"] .mermaid .label {
  color: var(--text-primary) !important;
  fill: var(--text-primary) !important;
}

[data-theme="light"] .mermaid .edgeLabel {
  background-color: #ffffff !important;
  color: var(--text-primary) !important;
}

[data-theme="light"] .mermaid .edgeLabel rect {
  fill: #ffffff !important;
}

[data-theme="light"] .mermaid .edgeLabel span,
[data-theme="light"] .mermaid .edgeLabel p {
  background-color: #ffffff !important;
  color: var(--text-primary) !important;
}

[data-theme="light"] .mermaid .edgePath .path,
[data-theme="light"] .mermaid .flowchart-link {
  stroke: var(--accent) !important;
}

[data-theme="light"] .mermaid .marker,
[data-theme="light"] .mermaid .arrowheadPath {
  fill: var(--accent) !important;
  stroke: var(--accent) !important;
}



/* ============================================
   Inline Code
   ============================================ */
.inline-code {
  background: var(--bg-code);
  padding: 0.125rem 0.375rem;
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 0.875em;
  color: var(--code-function);
}

/* ============================================
   Copy Button
   ============================================ */
.copy-btn {
  position: absolute;
  top: calc(var(--space-lg) + var(--space-md) + var(--space-xs));
  inset-inline-end: var(--space-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: var(--touch-target-min);
  min-height: var(--touch-target-min);
  padding: 0.375rem;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text-secondary);
  cursor: pointer;
  z-index: 10;
  opacity: 0;
  transition: opacity var(--transition-fast),
              background var(--transition-fast),
              color var(--transition-fast),
              border-color var(--transition-fast);
}

.code-content:hover .copy-btn,
.copy-btn:focus-visible {
  opacity: 1;
}

.copy-btn:hover {
  background: var(--bg-code);
  color: var(--accent);
  border-color: var(--accent);
}

.copy-btn:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.copy-btn.copied {
  color: var(--code-type);
  border-color: var(--code-type);
}

.copy-btn svg {
  width: 16px;
  height: 16px;
}

.copy-btn .check-icon { display: none; }
.copy-btn.copied .copy-icon { display: none; }
.copy-btn.copied .check-icon { display: block; }

/* ============================================
   Floating Navigation Widget
   ============================================ */
.float-nav {
  position: fixed;
  inset-inline-start: var(--space-md);
  inset-block-end: var(--space-md);
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
  z-index: 1000;
}

.float-nav-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: var(--touch-target-min);
  height: var(--touch-target-min);
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
  color: var(--text-secondary);
  text-decoration: none;
  transition: background var(--transition-fast),
              color var(--transition-fast),
              border-color var(--transition-fast),
              transform var(--transition-fast);
  position: relative;
}

.float-nav-btn:hover {
  background: var(--bg-code);
  color: var(--accent);
  border-color: var(--accent);
  transform: translateX(4px);
}

.float-nav-btn:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.float-nav-btn.active {
  background: rgba(88, 166, 255, 0.15);
  color: var(--accent);
  border-color: var(--accent);
}

.float-nav-btn svg {
  width: 20px;
  height: 20px;
}

/* Tooltip using CSS-only (no JS needed for hover) */
.float-nav-btn::after {
  content: attr(data-tooltip);
  position: absolute;
  inset-inline-start: calc(100% + 12px);
  top: 50%;
  transform: translateY(-50%);
  padding: var(--space-xs) var(--space-sm);
  background: var(--bg-secondary);
  color: var(--text-primary);
  font-size: var(--font-xs);
  font-weight: 500;
  white-space: nowrap;
  border: 1px solid var(--border);
  border-radius: 6px;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--transition-fast), visibility var(--transition-fast);
  pointer-events: none;
}

.float-nav-btn::before {
  content: '';
  position: absolute;
  inset-inline-start: calc(100% + 4px);
  top: 50%;
  transform: translateY(-50%);
  border: 6px solid transparent;
  border-inline-end-color: var(--border);
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--transition-fast), visibility var(--transition-fast);
  pointer-events: none;
}

.float-nav-btn:hover::after,
.float-nav-btn:hover::before,
.float-nav-btn:focus-visible::after,
.float-nav-btn:focus-visible::before {
  opacity: 1;
  visibility: visible;
}

/* ============================================
   Back to Top Button (Right side)
   ============================================ */
.back-to-top {
  position: fixed;
  inset-inline-end: var(--space-md);
  inset-block-end: var(--space-md);
  display: flex;
  align-items: center;
  justify-content: center;
  width: var(--touch-target-min);
  height: var(--touch-target-min);
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
  color: var(--text-secondary);
  cursor: pointer;
  z-index: 1000;
  opacity: 0;
  visibility: hidden;
  transition: background var(--transition-fast),
              color var(--transition-fast),
              border-color var(--transition-fast),
              transform var(--transition-fast),
              opacity var(--transition-fast),
              visibility var(--transition-fast);
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

.back-to-top:hover {
  background: var(--bg-code);
  color: var(--accent);
  border-color: var(--accent);
  transform: translateX(-4px);
}

.back-to-top:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.back-to-top svg {
  width: 20px;
  height: 20px;
}

/* Tooltip for back-to-top (appears on left) */
.back-to-top::after {
  content: attr(data-tooltip);
  position: absolute;
  inset-inline-end: calc(100% + 12px);
  top: 50%;
  transform: translateY(-50%);
  padding: var(--space-xs) var(--space-sm);
  background: var(--bg-secondary);
  color: var(--text-primary);
  font-size: var(--font-xs);
  font-weight: 500;
  white-space: nowrap;
  border: 1px solid var(--border);
  border-radius: 6px;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--transition-fast), visibility var(--transition-fast);
  pointer-events: none;
}

.back-to-top::before {
  content: '';
  position: absolute;
  inset-inline-end: calc(100% + 4px);
  top: 50%;
  transform: translateY(-50%);
  border: 6px solid transparent;
  border-inline-start-color: var(--border);
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--transition-fast), visibility var(--transition-fast);
  pointer-events: none;
}

.back-to-top:hover::after,
.back-to-top:hover::before,
.back-to-top:focus-visible::after,
.back-to-top:focus-visible::before {
  opacity: 1;
  visibility: visible;
}

/* ============================================
   Footer
   ============================================ */
footer {
  margin-block-start: var(--space-xl);
  padding: var(--space-lg);
  background: var(--bg-secondary);
  border-block-start: 1px solid var(--border);
  text-align: center;
  color: var(--text-secondary);
  font-size: var(--font-sm);
}

footer a {
  color: var(--accent);
  text-decoration: none;
  transition: color var(--transition-fast);
}

footer a:hover {
  text-decoration: underline;
}

footer a:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* ============================================
   Responsive Design - Tablet (max-width: 1024px)
   ============================================ */
@media (max-width: 1024px) {
  .doc-row {
    grid-template-columns: 1fr;
  }
}

/* ============================================
   Responsive Design - Mobile (max-width: 768px)
   ============================================ */
@media (max-width: 768px) {
  header {
    padding-inline: var(--space-sm);
    min-height: auto;
    padding-block: var(--space-sm);
  }
  
  header h1 {
    font-size: var(--font-md);
  }
  
  /* Show mobile menu button */
  .mobile-menu-btn {
    display: flex;
  }
  
  /* CSS-only mobile navigation */
  nav {
    position: absolute;
    top: 100%;
    inset-inline: 0;
    flex-direction: column;
    padding: var(--space-xs) var(--space-sm) var(--space-sm);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
    /* Hidden by default */
    display: none;
  }
  
  nav a {
    padding: var(--space-sm) var(--space-sm);
  }
  
  /* Show nav when checkbox is checked - checkbox is direct sibling before nav */
  #mobile-menu-toggle:checked + nav {
    display: flex;
  }
  
  /* Use :has() to change the icon in header when checkbox is checked */
  /* Note: :has() is supported in all modern browsers (2023+) */
  body:has(#mobile-menu-toggle:checked) .mobile-menu-btn .menu-icon {
    display: none;
  }
  
  body:has(#mobile-menu-toggle:checked) .mobile-menu-btn .close-icon {
    display: block;
  }
  
  main {
    padding: var(--space-sm);
  }
  
  .intro {
    padding: var(--space-md);
  }
  
  .architecture {
    padding: var(--space-sm);
  }
  
  /* Floating nav adjustments */
  .float-nav {
    inset-inline-start: var(--space-sm);
    inset-block-end: var(--space-sm);
  }
  
  .float-nav-btn {
    width: 40px;
    height: 40px;
  }
  
  .float-nav-btn svg {
    width: 18px;
    height: 18px;
  }
  
  /* Hide tooltips on mobile */
  .float-nav-btn::after,
  .float-nav-btn::before {
    display: none;
  }
  
  /* Back to top adjustments */
  .back-to-top {
    inset-inline-end: var(--space-sm);
    inset-block-end: var(--space-sm);
    width: 40px;
    height: 40px;
  }
  
  .back-to-top svg {
    width: 18px;
    height: 18px;
  }
  
  .back-to-top::after,
  .back-to-top::before {
    display: none;
  }
}

/* ============================================
   Responsive Design - Small Mobile (max-width: 480px)
   ============================================ */
@media (max-width: 480px) {
  :root {
    --space-md: 0.75rem;
    --space-lg: 1rem;
  }
  
  .features {
    grid-template-columns: 1fr;
  }
  
  .doc-content {
    padding: var(--space-sm);
  }
  
  .code-header {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.25rem;
  }
  
  pre {
    font-size: 0.7rem;
  }
  
  /* Hide floating nav on very small screens */
  .float-nav {
    display: none;
  }
}

/* ============================================
   Landscape Mobile Orientation
   ============================================ */
@media (max-width: 896px) and (orientation: landscape) {
  header {
    position: relative; /* Allow scrolling past header */
  }
  
  .float-nav {
    flex-direction: row;
    inset-block-end: var(--space-xs);
    inset-inline-start: 50%;
    transform: translateX(-50%);
  }
}

/* ============================================
   High Contrast Mode Support
   ============================================ */
@media (prefers-contrast: high) {
  :root {
    --border: #ffffff;
    --text-secondary: var(--text-primary);
  }
  
  [data-theme="light"] {
    --border: #000000;
  }
  
  .tag,
  nav a,
  .float-nav-btn,
  .back-to-top {
    border: 2px solid currentColor;
  }
}

/* ============================================
   Print Styles
   ============================================ */
@media print {
  header,
  nav,
  .float-nav,
  .back-to-top,
  .theme-toggle,
  .mobile-menu-btn,
  .mobile-menu-checkbox,
  .collapse-btn,
  .copy-btn {
    display: none !important;
  }
  
  main {
    max-width: none;
    padding: 0;
  }
  
  section {
    break-inside: avoid;
  }
  
  section.collapsed .section-content {
    max-height: none;
    opacity: 1;
  }
  
  .doc-row {
    grid-template-columns: 1fr;
  }
  
  a {
    text-decoration: underline;
  }
  
  a[href^="http"]::after {
    content: " (" attr(href) ")";
    font-size: 0.8em;
  }
}