:root {
    --board-size: 594px;
    --cell-size: 66px;
    --primary-color: #123456;
    --highlight-color: #a0c0e0;
    --error-color: #ff6666;
    --given-bg: #e0e0e0;
    --bg-color: #f0f0f0;
    --text-color: #333;
}

body {
    font-family: sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    background-color: var(--bg-color);
    margin: 0;
    padding: 10px;
}

h1 {
    color: var(--text-color);
}

#board {
    display: grid;
    grid-template-columns: repeat(9, var(--cell-size));
    grid-template-rows: repeat(9, var(--cell-size));
    width: var(--board-size);
    height: var(--board-size);
    border: 3px solid #000;
}

.cell {
    width: var(--cell-size);
    height: var(--cell-size);
    font-size: 32px;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    background-color: #fff;
    border: 1px solid #ccc;
    box-sizing: border-box;
    position: relative;
    transition: background-color 0.2s, transform 0.1s;
}

.cell:hover:not(.given) {
    background-color: #eef6ff;
}

.highlight {
    background-color: #eef6ff;
}

.main-number {
    color: var(--primary-color);
    font-weight: bold;
}

.notes {
    display: none;
}

.cell.notes-mode .notes {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    font-size: 12px;
    color: #888;
    padding: 2px;
}

.notes-mode .main-number {
    display: none;
}

.given {
    background-color: var(--given-bg);
    cursor: default;
}

.selected {
    background-color: var(--highlight-color);
}

.error {
    background-color: var(--error-color);
    color: #fff;
}

#numbers {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-top: 20px;
    flex-wrap: wrap;
}

.number-btn {
    width: var(--cell-size);
    height: var(--cell-size);
    font-size: 32px;
    cursor: pointer;
    border: 1px solid #ccc;
    background-color: #fff;
    display: flex;
    flex-direction: column;
    align-items: center;
    transition: transform 0.1s;
}

.number-btn:hover:not(:disabled) {
    transform: scale(1.05);
}

.number-btn:disabled {
    background-color: #e0e0e0;
    color: #aaa;
}

#controls {
    margin-top: 20px;
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
}

button {
    padding: 10px 20px;
    font-size: 18px;
    cursor: pointer;
    border: 1px solid #ccc;
    background-color: #fff;
    transition: background-color 0.2s;
}

button:hover:not(:disabled) {
    background-color: #ddd;
}

#message-bar {
    margin-top: 10px;
    color: var(--error-color);
    font-weight: bold;
}

.modal-overlay {
    display: none;
    position: fixed;
    top: 0; left: 0;
    width: 100%; height: 100%;
    background-color: rgba(0,0,0,0.7);
    justify-content: center;
    align-items: center;
}

.modal-content {
    background-color: #fff;
    padding: 30px;
    border-radius: 10px;
    text-align: center;
    animation: fadeIn 0.3s ease-in-out;
}

@keyframes fadeIn {
    from { opacity: 0; transform: scale(0.9); }
    to { opacity: 1; transform: scale(1); }
}

@media (max-width: 600px) {
    :root {
        --board-size: calc(100vw - 10px);
        --cell-size: calc((100vw - 10px) / 9);
    }
}
/* Línies gruixudes per separar els blocs 3×3 */
.cell {
    border: 1px solid #ccc;
}

.cell:nth-child(3n) {
    border-right: 3px solid #000;
}

.cell:nth-child(9n+1) {
    border-left: 3px solid #000;
}

.cell:nth-child(n+19):nth-child(-n+27),
.cell:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 3px solid #000;
}

.cell:nth-child(-n+9) {
    border-top: 3px solid #000;
}

/* Transició suau de colors */
body, .cell, button {
    transition: background-color 0.3s, color 0.3s, border-color 0.3s;
}

/* Mode fosc */
.dark-mode {
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --given-bg: #333;
    --highlight-color: #2a2a2a;
    --error-color: #ff6666;
    --primary-color: #90caf9;
}

.dark-mode body {
    background-color: var(--bg-color);
    color: var(--text-color);
}

.dark-mode .cell {
    background-color: var(--bg-color);
    color: var(--text-color);
    border-color: #555;
}

.dark-mode .given {
    background-color: var(--given-bg);
    color: var(--text-color);
}

.dark-mode .highlight {
    background-color: rgba(255, 255, 255, 0.1);
}

.dark-mode button {
    background-color: var(--primary-color);
    color: #000;
    border: none;
}

.dark-mode .error {
    background-color: var(--error-color);
}