/* ============================================================
   Sudoku — Game Styles
   ============================================================ */

.sd-controls {
    display: flex;
    gap: var(--space-sm);
    margin-bottom: var(--space-md);
}

.diff-btn {
    opacity: 0.5;
}
.diff-btn.active {
    opacity: 1;
    background: var(--color-primary);
    color: var(--color-bg);
}

/* ---- Board ---- */
.sd-board {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    grid-template-rows: repeat(9, 1fr);
    width: min(90vw, 420px);
    aspect-ratio: 1;
    background: var(--color-surface-3);
    border: 3px solid var(--color-surface-3);
    border-radius: var(--radius-md);
    gap: 1px;
    overflow: hidden;
}

.sd-cell {
    aspect-ratio: 1;
    background: var(--color-surface);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
    font-weight: 700;
    cursor: pointer;
    user-select: none;
    -webkit-user-select: none;
    transition: background var(--transition-fast);
    position: relative;
}

.sd-cell:hover {
    background: var(--color-surface-2);
}

.sd-cell.selected {
    background: var(--color-surface-3);
    box-shadow: inset 0 0 0 2px var(--color-primary);
}

.sd-cell.given {
    color: var(--color-text);
}

.sd-cell.user {
    color: var(--color-primary);
}

.sd-cell.error {
    color: var(--color-danger);
    animation: shake 300ms ease;
}

.sd-cell.highlight-same {
    background: rgba(0, 212, 255, 0.08);
}

/* 3x3 block borders */
.sd-cell:nth-child(3n) {
    border-right: 2px solid var(--color-surface-3);
}
.sd-cell:nth-child(9n) {
    border-right: none;
}
.sd-board .sd-cell:nth-child(n+19):nth-child(-n+27),
.sd-board .sd-cell:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 2px solid var(--color-surface-3);
}

/* ---- Numpad ---- */
.sd-numpad {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: var(--space-sm);
    margin-top: var(--space-md);
    width: min(90vw, 420px);
}

.num-btn {
    aspect-ratio: 1;
    background: var(--color-surface);
    border: 1px solid var(--color-surface-2);
    border-radius: var(--radius-md);
    color: var(--color-text);
    font-size: 1.2rem;
    font-weight: 700;
    cursor: pointer;
    transition: all var(--transition-fast);
    -webkit-tap-highlight-color: transparent;
}

.num-btn:hover {
    background: var(--color-surface-2);
    border-color: var(--color-primary);
}

.num-btn:active {
    background: var(--color-primary);
    color: var(--color-bg);
    transform: scale(0.93);
}

.erase-btn {
    color: var(--color-danger);
    font-size: 1rem;
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-4px); }
    75% { transform: translateX(4px); }
}

@media (max-width: 420px) {
    .sd-cell {
        font-size: 1rem;
    }
}