:root {
  --bg: #0f1117;
  --surface: #1a1d2e;
  --surface2: #252842;
  --border: #2e3150;
  --accent: #6c63ff;
  --accent2: #ff6584;
  --accent3: #43d9ad;
  --accent4: #ffd166;
  --text: #e2e8f0;
  --text-dim: #8892a4;
  --node-fill: #252842;
  --node-stroke: #6c63ff;
  --leaf-fill: #1e2d3d;
  --leaf-stroke: #43d9ad;
  --highlight: #ffd166;
  --danger: #ff6584;
  --success: #43d9ad;
  --font: 'Inter', system-ui, sans-serif;
  --mono: 'JetBrains Mono', 'Fira Code', monospace;
}

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

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--font);
  min-height: 100vh;
}

/* Nav */
nav {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 0 2rem;
  display: flex;
  align-items: center;
  gap: 2rem;
  height: 56px;
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav-brand {
  font-weight: 700;
  font-size: 1rem;
  color: var(--accent);
  text-decoration: none;
  white-space: nowrap;
}

.nav-links {
  display: flex;
  gap: 0.25rem;
  overflow-x: auto;
  scrollbar-width: none;
}

.nav-links::-webkit-scrollbar { display: none; }

.nav-link {
  color: var(--text-dim);
  text-decoration: none;
  font-size: 0.85rem;
  padding: 0.4rem 0.75rem;
  border-radius: 6px;
  transition: all 0.15s;
  white-space: nowrap;
}

.nav-link:hover, .nav-link.active {
  color: var(--text);
  background: var(--surface2);
}

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

/* Layout */
.page {
  max-width: 1400px;
  margin: 0 auto;
  padding: 2rem;
}

.page-header {
  margin-bottom: 2rem;
}

.page-title {
  font-size: 1.75rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.page-desc {
  color: var(--text-dim);
  font-size: 0.95rem;
  max-width: 600px;
}

.two-col {
  display: grid;
  grid-template-columns: 1fr 380px;
  gap: 1.5rem;
  align-items: start;
}

@media (max-width: 900px) {
  .two-col { grid-template-columns: 1fr; }
}

/* Cards */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.5rem;
}

.card-title {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-dim);
  margin-bottom: 1rem;
}

/* Controls */
.controls {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.input-row {
  display: flex;
  gap: 0.5rem;
  align-items: center;
}

.input-row label {
  font-size: 0.85rem;
  color: var(--text-dim);
  min-width: 80px;
}

input[type="number"], input[type="text"], select {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  padding: 0.5rem 0.75rem;
  font-size: 0.9rem;
  font-family: var(--mono);
  flex: 1;
  min-width: 0;
  transition: border-color 0.15s;
}

input:focus, select:focus {
  outline: none;
  border-color: var(--accent);
}

.btn {
  border: none;
  border-radius: 8px;
  padding: 0.5rem 1rem;
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s;
  font-family: var(--font);
  white-space: nowrap;
}

.btn-primary {
  background: var(--accent);
  color: white;
}

.btn-primary:hover { background: #5a52e0; }

.btn-danger {
  background: var(--danger);
  color: white;
}

.btn-danger:hover { opacity: 0.85; }

.btn-ghost {
  background: var(--surface2);
  color: var(--text);
  border: 1px solid var(--border);
}

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

.btn-success {
  background: var(--success);
  color: #0f1117;
}

.btn-success:hover { opacity: 0.85; }

.btn-sm {
  padding: 0.35rem 0.75rem;
  font-size: 0.8rem;
}

.btn-group {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

/* Step controls */
.step-controls {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  background: var(--surface2);
  border-radius: 10px;
  border: 1px solid var(--border);
}

.step-info {
  flex: 1;
  font-size: 0.85rem;
  color: var(--text-dim);
  text-align: center;
}

/* Visualization area */
.viz-area {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
}

.viz-canvas {
  width: 100%;
  overflow-x: auto;
  overflow-y: auto;
  min-height: 400px;
  position: relative;
}

svg text { font-family: var(--font); }

/* Explanation box */
.explanation {
  background: var(--surface2);
  border-left: 3px solid var(--accent);
  border-radius: 0 8px 8px 0;
  padding: 0.75rem 1rem;
  font-size: 0.875rem;
  line-height: 1.6;
  min-height: 60px;
  transition: all 0.3s;
}

.explanation.success { border-left-color: var(--success); }
.explanation.danger { border-left-color: var(--danger); }
.explanation.warning { border-left-color: var(--accent4); }

/* Stat badges */
.stats {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.stat {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.5rem 0.75rem;
  text-align: center;
  min-width: 80px;
}

.stat-val {
  font-size: 1.25rem;
  font-weight: 700;
  font-family: var(--mono);
  color: var(--accent);
}

.stat-lbl {
  font-size: 0.7rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Tabs */
.tabs {
  display: flex;
  gap: 0.25rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 1.5rem;
}

.tab {
  padding: 0.6rem 1rem;
  font-size: 0.875rem;
  color: var(--text-dim);
  cursor: pointer;
  border-bottom: 2px solid transparent;
  transition: all 0.15s;
  user-select: none;
}

.tab.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

.tab-panel { display: none; }
.tab-panel.active { display: block; }

/* Animations */
@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

@keyframes slideIn {
  from { opacity: 0; transform: translateY(-8px); }
  to { opacity: 1; transform: translateY(0); }
}

.animate-in {
  animation: slideIn 0.3s ease-out;
}

/* Legend */
.legend {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
  font-size: 0.8rem;
}

.legend-item {
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.legend-dot {
  width: 12px;
  height: 12px;
  border-radius: 3px;
}

/* Algo steps */
.algo-steps {
  font-size: 0.8rem;
  font-family: var(--mono);
  background: var(--surface2);
  border-radius: 8px;
  padding: 0.75rem;
  line-height: 1.8;
}

.algo-step { color: var(--text-dim); }
.algo-step.current { color: var(--accent4); font-weight: 700; }
.algo-step.done { color: var(--success); }

/* Index page grid */
.app-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.25rem;
  margin-top: 2.5rem;
}

.app-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.5rem;
  text-decoration: none;
  color: var(--text);
  transition: all 0.2s;
  display: block;
}

.app-card:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(108, 99, 255, 0.15);
}

.app-card-icon {
  font-size: 2rem;
  margin-bottom: 0.75rem;
}

.app-card-title {
  font-size: 1.1rem;
  font-weight: 700;
  margin-bottom: 0.4rem;
}

.app-card-desc {
  font-size: 0.85rem;
  color: var(--text-dim);
  line-height: 1.5;
}

.app-card-tags {
  display: flex;
  gap: 0.4rem;
  flex-wrap: wrap;
  margin-top: 0.75rem;
}

.tag {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 0.2rem 0.5rem;
  font-size: 0.7rem;
  color: var(--text-dim);
}

/* Hero */
.hero {
  text-align: center;
  padding: 4rem 2rem 2rem;
}

.hero-title {
  font-size: 2.5rem;
  font-weight: 800;
  background: linear-gradient(135deg, var(--accent), var(--accent3));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 1rem;
}

.hero-sub {
  font-size: 1.1rem;
  color: var(--text-dim);
  max-width: 500px;
  margin: 0 auto;
}