:root {
  color-scheme: light;
  /* Pure White Light Theme */
  --bg-primary: #ffffff;
  --bg-surface: #ffffff;
  --bg-surface-elevated: #f5f5f5;
  --bg-code: #f8f8f9;
  --text-primary: #0a0a0a;
  --text-secondary: #525252;
  --text-muted: #737373;
  --text-code: #171717;
  --border-color: #e5e5e5;
  --border-focus: #0a0a0a;
  --accent: #0a0a0a;
  --accent-hover: #262626;
  --accent-subtle: #f0f0f0;
  --badge-bg: #f4f4f5;
  --badge-text: #18181b;
  --success: #16a34a;
  --warning: #ca8a04;
  --danger: #dc2626;
  --radius-sm: 4px;
  --radius-md: 6px;
  --radius-lg: 8px;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 2px 4px rgba(0, 0, 0, 0.08);
  --font-ui: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  --font-code: 'JetBrains Mono', 'Fira Code', Consolas, monospace;
}

[data-theme='dark'] {
  color-scheme: dark;
  /* Pure Black Dark Theme (Neutral OLED Black, Zero Blue Tint) */
  --bg-primary: #000000;
  --bg-surface: #0a0a0a;
  --bg-surface-elevated: #171717;
  --bg-code: #050505;
  --text-primary: #ffffff;
  --text-secondary: #a3a3a3;
  --text-muted: #737373;
  --text-code: #f5f5f5;
  --border-color: #262626;
  --border-focus: #737373;
  --accent: #ffffff;
  --accent-hover: #e5e5e5;
  --accent-subtle: #1f1f1f;
  --badge-bg: #1c1c1c;
  --badge-text: #e5e5e5;
  --success: #22c55e;
  --warning: #eab308;
  --danger: #ef4444;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.6);
  --shadow-md: 0 4px 8px rgba(0, 0, 0, 0.8);
}

/* Reset */
*, *::before, *::after {
  box-sizing: border-box;
}

body, h1, h2, h3, p, margin, padding {
  margin: 0;
  padding: 0;
}

body {
  font-family: var(--font-ui);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.5;
}

/* Navbar */
.navbar {
  position: sticky;
  top: 0;
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  z-index: 100;
}

.navbar-container {
  max-width: 1400px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  padding: 16px;
}

.navbar-brand {
  font-weight: 700;
  text-decoration: none;
  color: var(--text-primary);
  font-size: 1.25rem;
  margin-right: 32px;
}

.navbar-nav {
  display: flex;
  gap: 24px;
}

.nav-link {
  text-decoration: none;
  color: var(--text-secondary);
  transition: color 150ms;
}

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

.nav-link.active {
  color: var(--accent);
  font-weight: 700;
}

.navbar-actions {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: 16px;
}

#search-input {
  padding: 8px 12px;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  background: var(--bg-surface-elevated);
  color: var(--text-primary);
}

#search-input:focus {
  outline: none;
  border-color: var(--border-focus);
}

.btn-icon {
  background: transparent;
  border: none;
  cursor: pointer;
  font-size: 1.2rem;
  padding: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Buttons */
.btn {
  padding: 8px 16px;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: background 150ms, border 150ms, color 150ms;
  font-family: var(--font-ui);
  font-size: 0.9rem;
}

.btn-secondary {
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  color: var(--text-primary);
}

.btn-secondary:hover {
  background: var(--bg-surface);
  border-color: var(--border-focus);
}

.btn-danger {
  background: transparent;
  border: 1px solid var(--danger);
  color: var(--danger);
}

.btn-danger:hover {
  background: var(--danger);
  color: var(--bg-surface);
}

/* Select Input */
.select-input {
  padding: 8px 12px;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  background: var(--bg-surface);
  color: var(--text-primary);
  font-family: var(--font-ui);
}

/* Layout */
.explorer-layout {
  display: grid;
  grid-template-columns: 280px 1fr;
  align-items: start;
  min-height: calc(100vh - 65px);
}

.sidebar {
  position: sticky;
  top: 65px;
  height: calc(100vh - 65px);
  max-height: calc(100vh - 65px);
  background: var(--bg-surface);
  border-right: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  padding: 0;
}

.sidebar-header {
  padding: 16px 20px;
  border-bottom: 1px solid var(--border-color);
  background: var(--bg-surface);
  flex-shrink: 0;
}

.sidebar-header h2 {
  font-size: 0.85rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.language-list {
  flex: 1;
  overflow-y: auto;
  padding: 12px;
}

.language-group {
  margin-bottom: 16px;
}

.category-title {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  padding: 8px 12px 4px;
}

.language-item {
  display: block;
  width: 100%;
  text-align: left;
  padding: 8px 12px;
  border: none;
  background: transparent;
  cursor: pointer;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-family: var(--font-ui);
  font-size: 1rem;
  transition: background 150ms, color 150ms;
  margin-bottom: 4px;
}

.language-item:hover {
  background: var(--bg-surface-elevated);
}

.language-item.active {
  color: var(--accent);
  background: var(--accent-subtle);
  font-weight: 500;
}

.content-area {
  padding: 32px;
}

.content-header {
  margin-bottom: 24px;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 16px;
}

.content-header h1 {
  font-size: 2rem;
  margin-bottom: 8px;
}

.language-meta {
  display: flex;
  gap: 8px;
}

.badge {
  display: inline-block;
  padding: 2px 8px;
  border-radius: var(--radius-sm);
  background: var(--badge-bg);
  color: var(--badge-text);
  font-size: 0.75rem;
  font-weight: 600;
}

.concepts-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(400px, 1fr));
  gap: 24px;
}

.concept-category-header {
  grid-column: 1 / -1;
  padding: 24px 0 8px;
  border-bottom: 1px solid var(--border-color);
  margin-top: 8px;
}

.concept-category-header:first-child {
  padding-top: 0;
  margin-top: 0;
}

.concept-category-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.01em;
}

.concept-card {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
}

.concept-card-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 16px;
  border-bottom: 1px solid var(--border-color);
}

.concept-title {
  font-size: 1.1rem;
  font-weight: 600;
}

.copy-btn {
  background: transparent;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  cursor: pointer;
  padding: 4px 8px;
  color: var(--text-secondary);
  font-size: 0.85rem;
  transition: border 150ms, color 150ms;
}

.copy-btn:hover {
  border-color: var(--border-focus);
  color: var(--text-primary);
}

.code-block {
  background: var(--bg-code);
  color: var(--text-code);
  padding: 16px;
  margin: 0;
  overflow-x: auto;
  font-family: var(--font-code);
  font-size: 0.875rem;
  line-height: 1.6;
}

.concept-notes {
  padding: 12px 16px;
  color: var(--text-secondary);
  font-size: 0.85rem;
  border-top: 1px solid var(--border-color);
}

/* Minimalist Custom Scrollbar */
.language-list::-webkit-scrollbar,
.code-block::-webkit-scrollbar {
  width: 5px;
  height: 5px;
}

.language-list::-webkit-scrollbar-track,
.code-block::-webkit-scrollbar-track {
  background: transparent;
}

.language-list::-webkit-scrollbar-thumb,
.code-block::-webkit-scrollbar-thumb {
  background: var(--border-color);
  border-radius: 4px;
}

.language-list::-webkit-scrollbar-thumb:hover,
.code-block::-webkit-scrollbar-thumb:hover {
  background: var(--text-muted);
}

.footer {
  text-align: center;
  padding: 24px;
  color: var(--text-muted);
  border-top: 1px solid var(--border-color);
  font-size: 0.9rem;
}

@media (max-width: 768px) {
  .explorer-layout {
    grid-template-columns: 1fr;
  }
  
  .sidebar {
    position: static;
    border-right: none;
    border-bottom: 1px solid var(--border-color);
    height: auto;
    max-height: 280px;
  }

  .language-list {
    max-height: 220px;
  }
  
  .concepts-grid {
    grid-template-columns: 1fr;
  }
}

/* Command Palette Trigger in Navbar */
.palette-trigger-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 6px 12px;
  color: var(--text-secondary);
  font-family: var(--font-ui);
  font-size: 0.85rem;
  cursor: pointer;
  transition: border 150ms, color 150ms, background 150ms;
}

.palette-trigger-btn:hover {
  border-color: var(--border-focus);
  color: var(--text-primary);
}

.palette-kbd {
  font-family: var(--font-code);
  font-size: 0.72rem;
  padding: 2px 6px;
  border-radius: var(--radius-sm);
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-muted);
}

/* Command Palette Overlay & Modal */
.palette-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.7);
  backdrop-filter: blur(2px);
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding-top: 12vh;
  z-index: 1000;
  opacity: 0;
  pointer-events: none;
  transition: opacity 150ms ease-in-out;
}

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

.palette-container {
  width: 90%;
  max-width: 600px;
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  box-shadow: 0 16px 40px rgba(0, 0, 0, 0.5);
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.palette-header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 18px;
  border-bottom: 1px solid var(--border-color);
  background: var(--bg-surface);
}

.palette-search-icon {
  font-size: 1rem;
  color: var(--text-muted);
}

.palette-input {
  flex: 1;
  background: transparent;
  border: none;
  outline: none;
  color: var(--text-primary);
  font-family: var(--font-ui);
  font-size: 1.05rem;
}

.palette-close-btn {
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  font-size: 0.72rem;
  padding: 2px 6px;
  font-family: var(--font-code);
  cursor: pointer;
}

.palette-results {
  max-height: 380px;
  overflow-y: auto;
  padding: 8px;
}

.palette-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 12px;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: background 120ms;
}

.palette-item.selected,
.palette-item:hover {
  background: var(--bg-surface-elevated);
}

.palette-item-icon {
  font-size: 1.1rem;
  opacity: 0.85;
}

.palette-item-content {
  flex: 1;
  min-width: 0;
}

.palette-item-title {
  color: var(--text-primary);
  font-size: 0.92rem;
  font-weight: 500;
}

.palette-item-subtitle {
  color: var(--text-muted);
  font-size: 0.78rem;
  margin-top: 2px;
}

.palette-item-badge {
  font-size: 0.72rem;
  padding: 2px 8px;
  border-radius: var(--radius-sm);
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-muted);
  white-space: nowrap;
}

.palette-empty {
  padding: 32px 16px;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.9rem;
}

.palette-footer {
  display: flex;
  gap: 16px;
  padding: 10px 18px;
  border-top: 1px solid var(--border-color);
  background: var(--bg-surface-elevated);
  font-size: 0.76rem;
  color: var(--text-muted);
}

.palette-hint kbd {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 3px;
  padding: 1px 4px;
  font-family: var(--font-code);
  margin-right: 4px;
}

/* Sidebar Header & Filter Chips */
.sidebar-title-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 10px;
}

.language-count {
  font-size: 0.75rem;
  font-family: var(--font-code);
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  padding: 1px 6px;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
}

.sidebar-search-box {
  margin-bottom: 10px;
}

.sidebar-search-input {
  width: 100%;
  padding: 6px 10px;
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-family: var(--font-ui);
  font-size: 0.85rem;
}

.sidebar-search-input:focus {
  outline: none;
  border-color: var(--border-focus);
}

.filter-chips {
  display: flex;
  gap: 6px;
  overflow-x: auto;
  padding-bottom: 4px;
}

.filter-chips::-webkit-scrollbar {
  height: 3px;
}

.filter-chip {
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 3px 8px;
  font-size: 0.72rem;
  color: var(--text-secondary);
  cursor: pointer;
  white-space: nowrap;
  transition: background 150ms, border 150ms, color 150ms;
}

.filter-chip:hover {
  border-color: var(--border-focus);
  color: var(--text-primary);
}

.filter-chip.active {
  background: var(--accent-subtle);
  border-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}

/* Action Buttons & Cross-Navigation */
.header-main-row {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
  flex-wrap: wrap;
}

.header-title-group {
  flex: 1;
}

.header-actions {
  display: flex;
  gap: 8px;
  align-items: center;
}

.action-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 12px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  background: var(--bg-surface-elevated);
  color: var(--text-secondary);
  font-size: 0.82rem;
  cursor: pointer;
  text-decoration: none;
  font-family: var(--font-ui);
  transition: border 150ms, color 150ms, background 150ms;
}

.action-btn:hover {
  border-color: var(--border-focus);
  color: var(--text-primary);
  background: var(--bg-surface);
}

.concept-card-actions {
  display: flex;
  gap: 6px;
  align-items: center;
}

.concept-action-btn {
  padding: 4px 8px;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  background: var(--bg-surface-elevated);
  color: var(--text-secondary);
  font-size: 0.78rem;
  text-decoration: none;
  cursor: pointer;
  font-family: var(--font-ui);
  transition: border 150ms, color 150ms, background 150ms;
}

.concept-action-btn:hover {
  border-color: var(--border-focus);
  color: var(--text-primary);
}

/* Playground / REPL Badge */
.playground-badge {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  text-decoration: none;
  background: var(--accent-subtle);
  border: 1px solid var(--accent);
  color: var(--accent);
  font-weight: 500;
  transition: opacity 150ms;
}

.playground-badge:hover {
  opacity: 0.85;
}