:root {
  --bg: #0d1117;
  --sidebar-bg: #090d13;
  --card-bg: #161b22;
  --border: #30363d;
  --text: #e6edf3;
  --text-muted: #8b949e;
  --accent: #2ea043;
  --accent-light: #3fb950;
  --accent-glow: rgba(46, 160, 67, 0.15);
  --code-bg: #161b22;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  min-height: 100vh;
}

.layout {
  display: flex;
  min-height: 100vh;
}

/* Sidebar */
.sidebar {
  width: 270px;
  background: var(--sidebar-bg);
  border-right: 1px solid var(--border);
  padding: 36px 20px 40px;
  flex-shrink: 0;
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
}

.sidebar-brand {
  margin-bottom: 28px;
}

.brand-title {
  font-size: 1.25rem;
  font-weight: 700;
  color: #ffffff;
  text-decoration: none;
  display: block;
}

.brand-subtitle {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: 4px;
}

.nav-hub {
  margin-bottom: 24px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--border);
}

.nav-hub a {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.85rem;
  font-weight: 600;
  padding: 6px 10px;
  border-radius: 6px;
  transition: all 0.15s ease;
}

.nav-hub a:hover {
  color: var(--text);
  background: rgba(255, 255, 255, 0.05);
}

.nav-label {
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin-bottom: 10px;
}

.nav-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 4px;
  flex: 1;
}

.nav-link {
  display: block;
  padding: 8px 12px;
  border-radius: 6px;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  transition: all 0.15s ease;
}

.nav-link:hover {
  color: var(--text);
  background: rgba(255, 255, 255, 0.05);
}

.nav-link.active {
  color: var(--accent-light);
  background: var(--accent-glow);
  font-weight: 600;
  border-left: 3px solid var(--accent-light);
}

.sidebar-footer {
  margin-top: auto;
  padding-top: 20px;
  border-top: 1px solid var(--border);
  font-size: 0.8rem;
}

.sidebar-footer a {
  color: var(--text-muted);
  text-decoration: none;
}

.sidebar-footer a:hover {
  color: var(--accent-light);
}

/* Main Content Area */
.content {
  flex: 1;
  max-width: 900px;
  padding: 56px 64px 80px;
}

h1 {
  font-size: 2.2rem;
  font-weight: 800;
  color: #ffffff;
  letter-spacing: -0.02em;
  margin-bottom: 12px;
}

.lead {
  font-size: 1.15rem;
  color: var(--text-muted);
  margin-bottom: 36px;
  line-height: 1.6;
}

h2 {
  font-size: 1.4rem;
  font-weight: 700;
  color: #ffffff;
  margin-top: 40px;
  margin-bottom: 16px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}

h3 {
  font-size: 1.1rem;
  font-weight: 600;
  color: #ffffff;
  margin-top: 28px;
  margin-bottom: 12px;
}

p {
  margin-bottom: 18px;
  color: var(--text);
}

ul, ol {
  margin-bottom: 20px;
  padding-left: 24px;
}

li {
  margin-bottom: 8px;
}

strong {
  color: #ffffff;
}

code {
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.875em;
  background: rgba(110, 118, 129, 0.2);
  padding: 2px 6px;
  border-radius: 4px;
  color: #e6edf3;
}

pre {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 16px 20px;
  margin-bottom: 24px;
  overflow-x: auto;
}

pre code {
  background: none;
  padding: 0;
  font-size: 0.875rem;
  line-height: 1.6;
  color: #e6edf3;
}

/* Badges */
.badge {
  display: inline-block;
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  padding: 3px 8px;
  border-radius: 12px;
  margin-left: 8px;
  vertical-align: middle;
  background: var(--accent-glow);
  color: var(--accent-light);
  border: 1px solid rgba(46, 160, 67, 0.4);
}

/* Concept Cards */
.concept-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 16px;
  margin: 28px 0;
}

.concept-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 20px;
  transition: all 0.2s ease;
}

.concept-card:hover {
  border-color: var(--accent-light);
  transform: translateY(-2px);
}

.concept-icon {
  font-size: 1.8rem;
  margin-bottom: 12px;
}

.concept-title {
  font-size: 1.1rem;
  font-weight: 700;
  color: #ffffff;
  margin-bottom: 6px;
}

.concept-role {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--accent-light);
  font-weight: 600;
  margin-bottom: 8px;
}

.concept-desc {
  font-size: 0.88rem;
  color: var(--text-muted);
  line-height: 1.5;
}

/* Tables */
table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: 28px;
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
}

th, td {
  padding: 12px 16px;
  text-align: left;
  border-bottom: 1px solid var(--border);
  font-size: 0.9rem;
}

th {
  background: var(--sidebar-bg);
  font-weight: 600;
  color: #ffffff;
}

td {
  background: var(--card-bg);
}

/* Callouts */
.note {
  background: rgba(46, 160, 67, 0.1);
  border-left: 3px solid var(--accent-light);
  padding: 16px 20px;
  border-radius: 0 6px 6px 0;
  margin: 24px 0;
  color: var(--text);
}

.note strong {
  color: var(--accent-light);
  display: block;
  margin-bottom: 6px;
}

/* Page Navigation */
.page-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}

.page-nav a {
  color: var(--accent-light);
  text-decoration: none;
  font-weight: 500;
  font-size: 0.95rem;
}

.page-nav a:hover {
  text-decoration: underline;
}

/* Interactive Playground Layout */
.playground-section {
  margin: 40px 0;
  padding: 24px;
  background: #090d13;
  border: 1px solid var(--border);
  border-radius: 12px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
}

.playground-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 16px;
  margin-bottom: 20px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--border);
}

.playground-title {
  font-size: 1.3rem;
  font-weight: 700;
  color: #ffffff;
  display: flex;
  align-items: center;
  gap: 10px;
}

.preset-controls {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.preset-label {
  font-size: 0.82rem;
  color: var(--text-muted);
  font-weight: 600;
}

.preset-select {
  background: var(--card-bg);
  color: var(--text);
  border: 1px solid var(--border);
  padding: 6px 12px;
  border-radius: 6px;
  font-size: 0.85rem;
  outline: none;
  cursor: pointer;
}

.preset-select:focus {
  border-color: var(--accent-light);
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--accent);
  color: #ffffff;
  border: none;
  padding: 7px 16px;
  border-radius: 6px;
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s ease;
}

.btn:hover {
  background: var(--accent-light);
}

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

.btn-secondary:hover {
  background: rgba(255, 255, 255, 0.08);
  border-color: var(--accent-light);
}

.playground-grid {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 16px;
}

@media (max-width: 1050px) {
  .playground-grid {
    grid-template-columns: 1fr;
  }
}

.pane {
  display: flex;
  flex-direction: column;
}

.pane-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 8px;
}

.pane-title {
  font-size: 0.82rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
}

.pane-editor {
  width: 100%;
  height: 380px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  color: #e6edf3;
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.84rem;
  line-height: 1.5;
  padding: 12px;
  resize: vertical;
  outline: none;
  box-sizing: border-box;
}

.pane-editor:focus {
  border-color: var(--accent-light);
}

.pane-editor.readonly {
  background: #11161d;
}

.status-bar {
  margin-top: 14px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8rem;
  color: var(--text-muted);
}

.status-indicator {
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.status-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--accent-light);
}

.status-dot.error {
  background: #f85149;
}

@media (max-width: 768px) {
  .layout {
    flex-direction: column;
  }
  .sidebar {
    width: 100%;
    height: auto;
    position: static;
  }
  .content {
    padding: 32px 20px 60px;
  }
}