
body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #f4f7f9;
    padding: 20px;
}

.container {
    background: white;
    padding: 30px;
    border-radius: 8px;
    box-shadow: 0 4px 10px rgba(0,0,0,0.1);
    text-align: center;
}

#generate-btn {
    padding: 12px 24px;
    font-size: 16px;
    cursor: pointer;
    background-color: #007bff;
    color: white;
    border: none;
    border-radius: 5px;
    transition: background-color 0.2s;
}

#generate-btn:disabled {
    background-color: #cccccc;
    cursor: not-allowed;
}

#generate-btn:hover:not(:disabled) {
    background-color: #0056b3;
}

#status-message {
    margin-top: 15px;
    font-size: 14px;
    color: #555;
    height: 20px;
}

#sudoku-board {
    display: grid;
    grid-template-columns: repeat(9, 40px);
    grid-template-rows: repeat(9, 40px);
    border: 3px solid #333;
    margin: 20px auto 0;
    width: 366px; /* (40px * 9) + 6px border */
}

.cell {
    width: 40px;
    height: 40px;
    border: 1px solid #ccc;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 20px;
    font-weight: bold;
    color: #333;
}

/* 3x3 구역을 위한 굵은 선 */
.cell:nth-child(3n) { border-right: 2px solid #333; }
.cell:nth-child(9n) { border-right: none; }
.cell:nth-of-type(n+19):nth-of-type(-n+27),
.cell:nth-of-type(n+46):nth-of-type(-n+54) {
    border-bottom: 2px solid #333;
}