:root {
    --bg: #0a0a12;
    --bg-card: #0f0f1e;
    --bg-card-hover: #161630;
    --text: #e4e4ef;
    --text-dim: #6e6e8e;
    --text-muted: #4a4a6a;
    --accent: #8b5cf6;
    --accent-glow: #a78bfa;
    --accent-subtle: rgba(139, 92, 246, 0.08);
    --border: #1c1c38;
    --border-focus: #8b5cf6;

    /* Node type colors */
    --node-reasoning: #6366f1;
    --node-exploration: #3b82f6;
    --node-backtrack: #f59e0b;
    --node-correction: #ef4444;
    --node-conclusion: #22c55e;
    --node-verification: #06b6d4;
    --node-default: #6e6e8e;

    --link-color: #2a2a4a;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    background: var(--bg);
    color: var(--text);
    min-height: 100vh;
    overflow-x: hidden;
    line-height: 1.6;
}

/* Header */
header {
    text-align: center;
    padding: 50px 20px 20px;
    background: linear-gradient(180deg, rgba(139, 92, 246, 0.05) 0%, transparent 100%);
}

header h1 {
    font-size: clamp(2rem, 5vw, 3.2rem);
    font-weight: 700;
    letter-spacing: -0.02em;
    background: linear-gradient(135deg, var(--text) 0%, var(--accent-glow) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 4px;
}

.subtitle {
    font-size: clamp(1rem, 2.5vw, 1.3rem);
    color: var(--accent-glow);
    font-weight: 300;
}

.subtitle-detail {
    font-size: 0.88rem;
    color: var(--text-dim);
    margin-top: 6px;
}

/* Input Section */
.input-section {
    max-width: 900px;
    margin: 30px auto 0;
    padding: 0 20px;
}

.input-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
    flex-wrap: wrap;
    gap: 10px;
}

.input-header h2 {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text);
}

.example-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.example-btn {
    padding: 5px 12px;
    font-size: 0.72rem;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 16px;
    color: var(--text-dim);
    cursor: pointer;
    transition: all 0.2s;
    font-family: inherit;
    white-space: nowrap;
}

.example-btn:hover {
    border-color: var(--accent);
    color: var(--accent-glow);
    background: var(--accent-subtle);
}

.example-btn .model-tag {
    font-size: 0.6rem;
    font-weight: 600;
    opacity: 0.6;
    margin-right: 3px;
}

.textarea-wrapper {
    position: relative;
}

textarea {
    width: 100%;
    height: 200px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 14px;
    color: var(--text);
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.82rem;
    padding: 18px;
    resize: vertical;
    outline: none;
    transition: border-color 0.2s;
    line-height: 1.7;
}

textarea:focus {
    border-color: var(--border-focus);
    box-shadow: 0 0 0 2px rgba(139, 92, 246, 0.1);
}

textarea::placeholder {
    color: var(--text-muted);
    font-style: italic;
}

.input-actions {
    display: flex;
    gap: 10px;
    margin-top: 12px;
}

.btn-primary {
    padding: 10px 28px;
    font-size: 0.88rem;
    font-weight: 600;
    background: var(--accent);
    color: white;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s;
    font-family: inherit;
}

.btn-primary:hover {
    background: #7c3aed;
    transform: translateY(-1px);
    box-shadow: 0 4px 20px rgba(139, 92, 246, 0.3);
}

.btn-secondary {
    padding: 10px 20px;
    font-size: 0.82rem;
    background: transparent;
    color: var(--text-dim);
    border: 1px solid var(--border);
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s;
    font-family: inherit;
}

.btn-secondary:hover {
    border-color: var(--text-dim);
    color: var(--text);
}

.keyboard-hint {
    font-size: 0.7rem;
    color: var(--text-muted);
    align-self: center;
    margin-left: 4px;
}

/* Stats Bar */
.stats-bar {
    max-width: 900px;
    margin: 24px auto 0;
    padding: 0 20px;
    display: flex;
    justify-content: center;
    gap: 32px;
    flex-wrap: wrap;
}

.stat-item {
    text-align: center;
}

.stat-value {
    font-family: 'JetBrains Mono', monospace;
    font-size: 1.6rem;
    font-weight: 700;
    color: var(--accent-glow);
    display: block;
    line-height: 1;
}

.stat-label {
    font-size: 0.7rem;
    color: var(--text-dim);
    text-transform: uppercase;
    letter-spacing: 0.08em;
    margin-top: 4px;
    display: block;
}

/* Legend */
.legend {
    max-width: 900px;
    margin: 16px auto 0;
    padding: 0 20px;
    display: flex;
    justify-content: center;
    gap: 20px;
    flex-wrap: wrap;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: 6px;
    font-size: 0.72rem;
    color: var(--text-dim);
}

.legend-dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
    flex-shrink: 0;
}

.legend-dot.reasoning { background: var(--node-reasoning); }
.legend-dot.exploration { background: var(--node-exploration); }
.legend-dot.backtrack { background: var(--node-backtrack); }
.legend-dot.correction { background: var(--node-correction); }
.legend-dot.conclusion { background: var(--node-conclusion); }
.legend-dot.verification { background: var(--node-verification); }

/* Visualization */
.viz-section {
    max-width: 100%;
    margin: 20px auto 0;
    padding: 0 20px;
    position: relative;
}

.viz-controls {
    position: absolute;
    top: 10px;
    right: 30px;
    display: flex;
    gap: 6px;
    z-index: 10;
}

.btn-icon {
    width: 34px;
    height: 34px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1rem;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 8px;
    color: var(--text-dim);
    cursor: pointer;
    transition: all 0.2s;
    font-family: inherit;
}

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

.viz-container {
    width: 100%;
    min-height: 500px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 14px;
    overflow: hidden;
    cursor: grab;
}

.viz-container:active {
    cursor: grabbing;
}

#tree-svg {
    width: 100%;
    min-height: 500px;
}

/* Tree nodes */
.node-group {
    cursor: pointer;
    transition: opacity 0.2s;
}

.node-group:hover {
    opacity: 0.9;
}

.node-circle {
    stroke-width: 2;
    transition: all 0.3s;
}

.node-group:hover .node-circle {
    stroke-width: 3;
    filter: drop-shadow(0 0 6px currentColor);
}

.node-label {
    font-family: 'Inter', sans-serif;
    font-size: 11px;
    fill: var(--text);
    pointer-events: none;
}

.node-type-badge {
    font-family: 'JetBrains Mono', monospace;
    font-size: 8px;
    fill: var(--text-dim);
    pointer-events: none;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.link-path {
    fill: none;
    stroke: var(--link-color);
    stroke-width: 1.5;
    opacity: 0.6;
}

.link-path.backtrack {
    stroke: var(--node-backtrack);
    stroke-dasharray: 5 3;
    opacity: 0.4;
}

/* Node collapse indicator */
.collapse-indicator {
    font-size: 9px;
    fill: var(--text-dim);
    pointer-events: none;
}

/* Detail Panel */
.detail-panel {
    position: fixed;
    bottom: 20px;
    right: 20px;
    width: 380px;
    max-height: 400px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 14px;
    box-shadow: 0 16px 48px rgba(0, 0, 0, 0.4);
    z-index: 100;
    overflow: hidden;
    display: flex;
    flex-direction: column;
}

.detail-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 14px 18px;
    border-bottom: 1px solid var(--border);
}

.detail-type {
    font-size: 0.72rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    padding: 3px 10px;
    border-radius: 6px;
}

.detail-type.reasoning { background: rgba(99, 102, 241, 0.15); color: var(--node-reasoning); }
.detail-type.exploration { background: rgba(59, 130, 246, 0.15); color: var(--node-exploration); }
.detail-type.backtrack { background: rgba(245, 158, 11, 0.15); color: var(--node-backtrack); }
.detail-type.correction { background: rgba(239, 68, 68, 0.15); color: var(--node-correction); }
.detail-type.conclusion { background: rgba(34, 197, 94, 0.15); color: var(--node-conclusion); }
.detail-type.verification { background: rgba(6, 182, 212, 0.15); color: var(--node-verification); }

.detail-close {
    width: 28px;
    height: 28px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: none;
    border: none;
    color: var(--text-dim);
    font-size: 1.2rem;
    cursor: pointer;
    border-radius: 6px;
    transition: all 0.2s;
}

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

.detail-content {
    padding: 16px 18px;
    overflow-y: auto;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.78rem;
    line-height: 1.7;
    color: var(--text);
    white-space: pre-wrap;
    word-break: break-word;
}

/* Hidden */
.hidden {
    display: none !important;
}

/* Footer */
footer {
    text-align: center;
    padding: 40px 20px;
    border-top: 1px solid var(--border);
    margin-top: 40px;
}

footer p {
    color: var(--text-dim);
    font-size: 0.8rem;
    margin-bottom: 6px;
}

.footer-note {
    font-size: 0.7rem !important;
    opacity: 0.5;
}

/* Scrollbar */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--accent); }

/* Responsive */
@media (max-width: 768px) {
    header { padding: 35px 16px 16px; }
    .input-header { flex-direction: column; align-items: flex-start; }
    .stats-bar { gap: 16px; }
    .stat-value { font-size: 1.3rem; }
    .detail-panel { width: calc(100% - 24px); left: 12px; right: 12px; }
    .legend { gap: 12px; }
    #tree-svg { min-height: 400px; }
}

@media (max-width: 480px) {
    .example-buttons { gap: 6px; }
    .example-btn { font-size: 0.65rem; padding: 4px 8px; }
    .stats-bar { gap: 12px; }
    .stat-value { font-size: 1.1rem; }
    textarea { height: 160px; font-size: 0.75rem; }
    .detail-panel { max-height: 300px; }
}