/* Binary Tree Visualizer - CS Textbook Dark Mode */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap');

:root {
  --primary: #00B4D8;
  --primary-dim: rgba(0, 180, 216, 0.15);
  --accent: #FF6B6B;
  --accent-dim: rgba(255, 107, 107, 0.15);
  --bg: #0A0F1A;
  --bg-card: rgba(15, 22, 40, 0.85);
  --bg-elevated: rgba(20, 30, 55, 0.9);
  --surface: rgba(30, 42, 70, 0.6);
  --text: #E8ECF4;
  --text-dim: #8892A8;
  --text-muted: #5A6480;
  --success: #4ADE80;
  --warning: #FBBF24;
  --red-node: #E74C3C;
  --black-node: #2C3E50;
  --border: rgba(100, 120, 160, 0.15);
  --glass: rgba(15, 22, 40, 0.7);
  --radius: 12px;
  --radius-sm: 8px;
  --radius-xs: 6px;
  --shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
  --transition: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
  font-family: 'Inter', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  overflow: hidden;
}

/* Header */
.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 20px;
  background: var(--glass);
  backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
  z-index: 100;
}

.header-left { display: flex; align-items: center; gap: 12px; }
.logo {
  width: 36px; height: 36px;
  background: linear-gradient(135deg, var(--primary), #0077B6);
  border-radius: var(--radius-sm);
  display: flex; align-items: center; justify-content: center;
  font-size: 18px; font-weight: 700; color: #fff;
}

.header h1 {
  font-size: 16px; font-weight: 600;
  background: linear-gradient(135deg, var(--primary), #90E0EF);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
}

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

/* Buttons */
.btn {
  padding: 7px 14px;
  border-radius: var(--radius-xs);
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-family: 'Inter', sans-serif;
  font-size: 12px; font-weight: 500;
  cursor: pointer;
  transition: var(--transition);
  display: inline-flex; align-items: center; gap: 6px;
  white-space: nowrap;
}
.btn:hover { background: rgba(50, 65, 100, 0.6); border-color: var(--primary); }
.btn-primary {
  background: linear-gradient(135deg, var(--primary), #0077B6);
  border-color: transparent; color: #fff;
}
.btn-primary:hover { filter: brightness(1.15); }
.btn-accent {
  background: linear-gradient(135deg, var(--accent), #E05555);
  border-color: transparent; color: #fff;
}
.btn-accent:hover { filter: brightness(1.15); }
.btn-sm { padding: 5px 10px; font-size: 11px; }
.btn.active { background: var(--primary-dim); border-color: var(--primary); color: var(--primary); }

/* Layout */
.app-layout {
  display: flex;
  height: calc(100vh - 61px);
}

/* Sidebar */
.sidebar {
  width: 280px;
  min-width: 280px;
  background: var(--glass);
  backdrop-filter: blur(20px);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  overflow-y: auto;
}

.sidebar-section {
  padding: 16px;
  border-bottom: 1px solid var(--border);
}

.sidebar-section h3 {
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text-dim);
  margin-bottom: 10px;
}

/* Tree Type Selector */
.tree-types { display: flex; flex-direction: column; gap: 4px; }
.tree-type-btn {
  padding: 8px 12px;
  border-radius: var(--radius-xs);
  border: 1px solid transparent;
  background: transparent;
  color: var(--text-dim);
  font-family: 'Inter', sans-serif;
  font-size: 13px; font-weight: 500;
  cursor: pointer;
  transition: var(--transition);
  text-align: left;
  display: flex; align-items: center; gap: 8px;
}
.tree-type-btn:hover { background: var(--surface); color: var(--text); }
.tree-type-btn.active {
  background: var(--primary-dim);
  border-color: var(--primary);
  color: var(--primary);
}
.tree-type-btn .badge {
  font-size: 10px;
  padding: 2px 6px;
  border-radius: 10px;
  background: var(--surface);
  color: var(--text-muted);
  margin-left: auto;
}

/* Input Groups */
.input-group { display: flex; gap: 6px; margin-bottom: 8px; }
.input-field {
  flex: 1;
  padding: 8px 12px;
  border-radius: var(--radius-xs);
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  font-family: 'JetBrains Mono', monospace;
  font-size: 13px;
  outline: none;
  transition: var(--transition);
}
.input-field:focus { border-color: var(--primary); box-shadow: 0 0 0 3px var(--primary-dim); }
.input-field::placeholder { color: var(--text-muted); }

/* Operation Buttons */
.op-buttons { display: flex; flex-wrap: wrap; gap: 4px; }
.op-buttons .btn { flex: 1; min-width: 70px; justify-content: center; }

/* Traversal Buttons */
.traversal-buttons { display: grid; grid-template-columns: 1fr 1fr; gap: 4px; }

/* Stats */
.stats-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 6px;
}
.stat-item {
  padding: 8px 10px;
  background: var(--surface);
  border-radius: var(--radius-xs);
  text-align: center;
}
.stat-value {
  font-family: 'JetBrains Mono', monospace;
  font-size: 18px; font-weight: 700;
  color: var(--primary);
}
.stat-label {
  font-size: 10px;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-top: 2px;
}

/* Canvas Area */
.canvas-area {
  flex: 1;
  position: relative;
  overflow: hidden;
  background:
    radial-gradient(circle at 20% 30%, rgba(0, 180, 216, 0.03) 0%, transparent 50%),
    radial-gradient(circle at 80% 70%, rgba(255, 107, 107, 0.03) 0%, transparent 50%),
    var(--bg);
}

#treeCanvas {
  width: 100%;
  height: 100%;
  display: block;
  cursor: grab;
}
#treeCanvas:active { cursor: grabbing; }

/* Canvas Toolbar */
.canvas-toolbar {
  position: absolute;
  bottom: 16px;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  gap: 4px;
  padding: 6px;
  background: var(--glass);
  backdrop-filter: blur(20px);
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

/* Info Panel */
.info-panel {
  position: absolute;
  top: 16px;
  right: 16px;
  background: var(--glass);
  backdrop-filter: blur(20px);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  padding: 14px;
  min-width: 200px;
  font-size: 12px;
  max-height: 300px;
  overflow-y: auto;
}
.info-panel h4 {
  font-size: 11px; font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--text-dim);
  margin-bottom: 8px;
}
.info-panel .step {
  padding: 4px 0;
  color: var(--text-dim);
  font-family: 'JetBrains Mono', monospace;
  font-size: 11px;
  border-bottom: 1px solid var(--border);
}
.info-panel .step.active { color: var(--primary); font-weight: 600; }
.info-panel .step.done { color: var(--success); }

/* Toast */
.toast {
  position: fixed;
  bottom: 80px;
  left: 50%;
  transform: translateX(-50%) translateY(20px);
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 10px 20px;
  font-size: 13px;
  color: var(--text);
  opacity: 0;
  transition: all 0.3s ease;
  z-index: 200;
  pointer-events: none;
}
.toast.show { opacity: 1; transform: translateX(-50%) translateY(0); }
.toast.success { border-color: var(--success); color: var(--success); }
.toast.error { border-color: var(--accent); color: var(--accent); }

/* Scrollbar */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--surface); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: rgba(50, 65, 100, 0.8); }

/* Responsive */
@media (max-width: 768px) {
  .app-layout { flex-direction: column; }
  .sidebar {
    width: 100%; min-width: unset;
    max-height: 40vh; flex-direction: row;
    flex-wrap: wrap; overflow-x: auto;
    border-right: none; border-bottom: 1px solid var(--border);
  }
  .sidebar-section { min-width: 240px; flex: 1; border-bottom: none; border-right: 1px solid var(--border); }
  .canvas-area { min-height: 50vh; }
}

@media (max-width: 480px) {
  .header h1 { font-size: 14px; }
  .sidebar-section { min-width: 200px; padding: 12px; }
}