:root {
    --bg: #0f172a;
    --panel-bg: rgba(30, 41, 59, 0.85);
    --panel-border: rgba(255, 255, 255, 0.08);
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --accent: #3b82f6;
    --primary: #3b82f6;
    --secondary: #f59e0b;
    --block-empty-bg: rgba(255, 255, 255, 0.04);
    --block-empty-border: rgba(255, 255, 255, 0.12);
}

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

body {
    font-family: 'Outfit', sans-serif;
    background-color: var(--bg);
    color: var(--text-primary);
    display: flex;
    height: 100vh;
    overflow: hidden;
}

/* ── Panel ── */
#ui-panel {
    width: 260px;
    flex-shrink: 0;
    background: var(--panel-bg);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-right: 1px solid var(--panel-border);
    display: flex;
    flex-direction: column;
    gap: 24px;
    padding: 24px 20px;
    overflow-y: auto;
}

.back-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.85rem;
    transition: color 0.2s;
}
.back-link:hover { color: var(--text-primary); }

.app-title {
    font-size: 1.4rem;
    font-weight: 600;
    color: var(--text-primary);
    line-height: 1.2;
}

.section-label {
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--text-secondary);
    margin-bottom: 10px;
}

/* ── Number controls ── */
.number-control {
    display: flex;
    align-items: center;
    gap: 10px;
}

.adjust-btn {
    width: 36px;
    height: 36px;
    border-radius: 8px;
    border: 1px solid var(--panel-border);
    background: rgba(255, 255, 255, 0.06);
    color: var(--text-primary);
    font-size: 1.2rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background 0.15s, transform 0.1s;
    user-select: none;
}
.adjust-btn:hover { background: rgba(255, 255, 255, 0.12); }
.adjust-btn:active { transform: scale(0.92); }

.number-display {
    flex: 1;
    text-align: center;
    font-size: 1.6rem;
    font-weight: 600;
    color: var(--text-primary);
    min-width: 60px;
}

/* ── Sum ── */
.sum-section {
    display: flex;
    align-items: baseline;
    gap: 8px;
    padding: 12px 0;
    border-top: 1px solid var(--panel-border);
    border-bottom: 1px solid var(--panel-border);
}
.sum-equals {
    font-size: 1.4rem;
    color: var(--text-secondary);
}
.sum-value {
    font-size: 2rem;
    font-weight: 600;
    color: var(--text-primary);
}

/* ── Legend ── */
.legend {
    display: flex;
    flex-direction: column;
    gap: 8px;
}
.legend-item {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 0.95rem;
    color: var(--text-secondary);
}
.legend-swatch {
    width: 18px;
    height: 18px;
    border-radius: 4px;
    flex-shrink: 0;
}
.legend-swatch.primary { background: var(--primary); }
.legend-swatch.secondary { background: var(--secondary); }

/* ── Main area ── */
#blocks-area {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 40px;
    overflow: auto;
}

#groups-container {
    display: flex;
    flex-direction: row;
    gap: 20px;
    align-items: flex-end;
}

/* ── Block groups ── */
.block-group {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0;
}

.blocks-stack {
    display: flex;
    flex-direction: column-reverse;
    gap: 3px;
    height: 387px; /* 10 × 36 + 9 × 3 */
    justify-content: flex-start;
}

.block {
    width: 36px;
    height: 36px;
    border-radius: 6px;
    flex-shrink: 0;
    transition: background 0.2s, border-color 0.2s;
}

.block.primary {
    background: var(--primary);
    box-shadow: 0 0 8px rgba(59, 130, 246, 0.35);
}

.block.secondary {
    background: var(--secondary);
    box-shadow: 0 0 8px rgba(245, 158, 11, 0.35);
}

.block.empty {
    background: var(--block-empty-bg);
    border: 1px dashed var(--block-empty-border);
    box-shadow: none;
}

.group-label {
    margin-top: 8px;
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-align: center;
}
.group-label.full {
    color: var(--text-secondary);
}
.group-label.decimal {
    color: var(--text-primary);
}