/* ============ Reset & Base ============ */
* { margin: 0; padding: 0; box-sizing: border-box; }

:root {
    --bg-primary: #001633;
    --bg-secondary: #0A2540;
    --bg-card: #0E2A47;
    --text-primary: #FFFFFF;
    --text-secondary: #78909C;
    --accent: #FFAB40;
    --accent-glow: rgba(255, 171, 64, 0.25);
    --accent2: #85D5E6;
    --success: #0097A7;
    --border: #1A3A5C;
    --sq-light: #B58863;
    --sq-dark: #6F4E37;
}

body {
    background: var(--bg-primary);
    color: var(--text-primary);
    font-family: Arial, 'Segoe UI', system-ui, -apple-system, sans-serif;
    min-height: 100vh;
    overflow-x: hidden;
}

/* ============ Header ============ */
.back-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.9rem;
    font-weight: 500;
    transition: color 0.2s;
}
.back-link:hover { color: var(--accent); }

header {
    display: flex;
    align-items: center;
    padding: 12px 24px;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    gap: 20px;
}

.header-left {
    display: flex;
    align-items: center;
    gap: 12px;
}

.header-logo {
    width: 32px;
    height: 32px;
    object-fit: contain;
}

header h1 {
    font-size: 1.2rem;
    font-weight: 600;
    letter-spacing: -0.02em;
    flex: 1;
}

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

.controls button {
    padding: 6px 16px;
    border: 1px solid var(--border);
    border-radius: 6px;
    background: var(--bg-card);
    color: var(--text-primary);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
}

.controls button:hover {
    background: var(--accent);
    border-color: var(--accent);
    color: var(--bg-primary);
}

.depth-group {
    display: flex;
    align-items: center;
    gap: 4px;
    margin-left: 8px;
}

.depth-group label {
    font-size: 0.8rem;
    color: var(--text-secondary);
    margin-right: 4px;
}

.depth-btn {
    padding: 4px 10px !important;
    font-size: 0.75rem !important;
}

.depth-btn.active {
    background: var(--accent) !important;
    border-color: var(--accent) !important;
    color: var(--bg-primary) !important;
}

/* ============ Main Layout ============ */
main {
    display: grid;
    grid-template-columns: auto 1fr;
    height: calc(100vh - 53px - 300px);
    min-height: 500px;
}

/* ============ Board Panel ============ */
.board-panel {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 16px 20px;
    background: var(--bg-secondary);
    border-right: 1px solid var(--border);
    gap: 12px;
}

.board-panel h2 {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    align-self: flex-start;
}

/* ============ Board Labels ============ */
.board-outer {
    display: flex;
    gap: 4px;
    align-items: stretch;
}

.board-col {
    display: flex;
    flex-direction: column;
}

.rank-labels {
    display: flex;
    flex-direction: column;
    justify-content: space-around;
    height: 400px;
    padding: 0 4px;
}

.rank-labels span {
    font-size: 0.72rem;
    color: var(--text-secondary);
    text-align: center;
    line-height: 50px;
    height: 50px;
}

.file-labels {
    display: grid;
    grid-template-columns: repeat(8, 50px);
    width: 400px;
    padding-top: 2px;
}

.file-labels span {
    font-size: 0.72rem;
    color: var(--text-secondary);
    text-align: center;
}

/* ============ Chess Board ============ */
.chess-board {
    display: grid;
    grid-template-columns: repeat(8, 50px);
    grid-template-rows: repeat(8, 50px);
    width: 400px;
    height: 400px;
    border: 2px solid var(--border);
    border-radius: 4px;
    overflow: hidden;
    flex-shrink: 0;
}

.square {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2.2rem;
    line-height: 1;
    width: 50px;
    height: 50px;
    cursor: pointer;
    user-select: none;
    position: relative;
    transition: background-color 0.15s;
    overflow: hidden;
}

.square.light { background: var(--sq-light); }
.square.dark { background: var(--sq-dark); }

.square:hover {
    filter: brightness(1.15);
}

.square.selected {
    background: rgba(255, 171, 64, 0.55) !important;
}

.square.last-move {
    background: rgba(133, 213, 230, 0.25) !important;
}

.square.check {
    background: rgba(232, 93, 74, 0.5) !important;
}

.square.move-target::after {
    content: "";
    width: 28%;
    height: 28%;
    border-radius: 50%;
    background: rgba(0, 0, 0, 0.3);
    position: absolute;
}

.square.capture-target::after {
    content: "";
    width: 90%;
    height: 90%;
    border-radius: 50%;
    border: 3px solid rgba(0, 0, 0, 0.3);
    background: transparent;
    position: absolute;
}

.white-piece {
    color: #fff;
    text-shadow: 0 0 2px rgba(0,0,0,0.6), 0 1px 3px rgba(0,0,0,0.4);
}
.black-piece {
    color: #1a1a1a;
    text-shadow: 0 0 2px rgba(255,255,255,0.15);
}

/* ============ Game Status ============ */
.game-status {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--accent);
    min-height: 1.2em;
    text-align: center;
}

.game-status.error {
    color: #e85d4a;
}

/* ============ Move History ============ */
.move-history {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 10px 12px;
    width: 400px;
    max-height: 120px;
    overflow-y: auto;
    font-size: 0.8rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

.move-history .move-pair {
    display: inline;
}

.move-history .move-num {
    color: var(--text-secondary);
    opacity: 0.6;
    margin-right: 2px;
}

.move-history .move-white {
    color: var(--text-primary);
    font-weight: 500;
    margin-right: 6px;
}

.move-history .move-black {
    color: var(--accent2);
    font-weight: 500;
    margin-right: 10px;
}

/* ============ Editor Panel ============ */
.editor-panel {
    padding: 16px 20px;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    gap: 14px;
}

.editor-panel h2 {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* ============ Preset Buttons ============ */
.preset-group {
    display: flex;
    align-items: center;
    gap: 6px;
    flex-wrap: wrap;
}

.preset-group label {
    font-size: 0.78rem;
    color: var(--text-secondary);
}

.preset-btn {
    padding: 4px 10px;
    border: 1px solid var(--border);
    border-radius: 4px;
    background: var(--bg-card);
    color: var(--text-primary);
    font-size: 0.75rem;
    cursor: pointer;
    transition: all 0.2s;
}

.preset-btn:hover {
    background: var(--accent);
    border-color: var(--accent);
    color: var(--bg-primary);
}

/* ============ Code Editor ============ */
.eval-editor-wrapper {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 10px;
    padding: 14px;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

#eval-editor {
    width: 100%;
    height: 320px;
    background: #0a0e14;
    color: #b3b1ad;
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 12px;
    font-family: "Consolas", "Monaco", "Courier New", monospace;
    font-size: 0.8rem;
    line-height: 1.55;
    resize: vertical;
    tab-size: 4;
    white-space: pre;
    overflow-wrap: normal;
    overflow-x: auto;
}

#eval-editor:focus {
    outline: none;
    border-color: var(--accent);
}

.editor-actions {
    display: flex;
    align-items: center;
    gap: 10px;
}

.editor-actions button {
    padding: 6px 16px;
    border: 1px solid var(--border);
    border-radius: 6px;
    background: var(--bg-card);
    color: var(--text-primary);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
}

.editor-actions button:hover {
    background: var(--accent);
    border-color: var(--accent);
    color: var(--bg-primary);
}

.eval-status {
    font-size: 0.78rem;
    padding: 4px 8px;
    border-radius: 4px;
}

.eval-status.valid {
    color: var(--success);
    background: rgba(0, 151, 167, 0.1);
}

.eval-status.invalid {
    color: #e85d4a;
    background: rgba(232, 93, 74, 0.1);
}

/* ============ Doc Panel ============ */
.doc-panel {
    width: 100%;
    height: 320px;
    background: #0a0e14;
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 12px;
    overflow-y: auto;
}

.doc-content h3 {
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--accent);
    margin: 12px 0 6px 0;
    text-transform: uppercase;
    letter-spacing: 0.03em;
}

.doc-content h3:first-child {
    margin-top: 0;
}

.doc-content dl {
    margin: 0;
}

.doc-content dt {
    font-family: "Consolas", "Monaco", "Courier New", monospace;
    font-size: 0.78rem;
    color: var(--accent2);
    font-weight: 600;
    margin-top: 6px;
}

.doc-content dd {
    font-size: 0.76rem;
    color: var(--text-secondary);
    margin-left: 12px;
    margin-bottom: 2px;
    line-height: 1.4;
}

/* ============ Save Feedback ============ */
.editor-actions .save-feedback {
    font-size: 0.78rem;
    color: var(--success);
    opacity: 0;
    transition: opacity 0.3s;
}

.editor-actions .save-feedback.visible {
    opacity: 1;
}

/* ============ Stats ============ */
.stats {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 10px;
    padding: 14px;
}

.stat-row {
    display: flex;
    justify-content: space-between;
    padding: 5px 0;
    border-bottom: 1px solid var(--border);
}

.stat-row:last-child { border-bottom: none; }

.stat-label {
    font-size: 0.82rem;
    color: var(--text-secondary);
}

.stat-value {
    font-size: 0.82rem;
    font-weight: 700;
    color: var(--accent);
    font-variant-numeric: tabular-nums;
}

/* ============ Info Text ============ */
.info-text {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 10px;
    padding: 14px;
}

.info-text p {
    font-size: 0.82rem;
    color: var(--text-secondary);
    line-height: 1.5;
    margin-bottom: 6px;
}

.info-text p:last-child { margin-bottom: 0; }

/* ============ Thinking Overlay ============ */
.thinking-overlay {
    position: absolute;
    inset: 0;
    background: rgba(0, 22, 51, 0.6);
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 4px;
    z-index: 10;
}

.thinking-text {
    color: var(--accent);
    font-size: 1rem;
    font-weight: 600;
    animation: pulse 1.2s ease-in-out infinite;
}

@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.4; }
}

/* ============ Tree Section ============ */
.tree-section {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border);
    padding: 14px 20px;
    min-height: 300px;
}

.tree-header {
    display: flex;
    align-items: center;
    gap: 14px;
    margin-bottom: 12px;
}

.tree-header h2 {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.tree-header button {
    padding: 4px 12px;
    border: 1px solid var(--border);
    border-radius: 4px;
    background: var(--bg-card);
    color: var(--text-primary);
    font-size: 0.75rem;
    cursor: pointer;
    transition: all 0.2s;
}

.tree-header button:hover {
    background: var(--accent);
    border-color: var(--accent);
    color: var(--bg-primary);
}

.tree-legend {
    display: flex;
    gap: 16px;
    margin-left: auto;
    font-size: 0.72rem;
    color: var(--text-secondary);
}

.tree-legend-item {
    display: flex;
    align-items: center;
    gap: 5px;
}

.legend-swatch {
    width: 14px;
    height: 10px;
    border-radius: 2px;
    border: 1.5px solid;
}

.legend-swatch.max-node {
    background: #1a2a40;
    border-color: var(--accent);
}

.legend-swatch.min-node {
    background: #0a2a3a;
    border-color: var(--accent2);
}

.legend-swatch.best-path {
    background: #2a3a20;
    border-color: var(--accent);
    border-width: 2.5px;
}

.legend-swatch.pruned {
    background: #0a1520;
    border-color: #555;
    border-style: dashed;
}

.tree-container {
    overflow-x: auto;
    overflow-y: auto;
    max-height: 450px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 10px;
}

.tree-container.collapsed {
    display: none;
}

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

.tree-empty {
    color: var(--text-secondary);
    font-size: 0.85rem;
    text-align: center;
    padding: 40px 0;
    opacity: 0.6;
}

/* ============ Board Wrapper ============ */
.board-wrapper {
    position: relative;
    display: inline-block;
}

/* ============ Responsive ============ */
@media (max-width: 900px) {
    main {
        grid-template-columns: 1fr;
        grid-template-rows: auto 1fr;
        height: auto;
    }
    .board-panel {
        border-right: none;
        border-bottom: 1px solid var(--border);
    }
    .chess-board {
        width: min(400px, 90vw);
        height: min(400px, 90vw);
    }
    .move-history { width: min(400px, 90vw); }
}