body {
    font-family: 'Arial', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
}

.container {
    background: white;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
    text-align: center;
    width: 400px; /* Increase width */
}

h1 {
    margin: 0 0 10px;
    font-size: 24px;
    color: #333;
}

#timer {
    margin-bottom: 20px;
    font-size: 18px;
    color: #555;
}

#sudoku-board {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    grid-gap: 1px;
    
    margin-bottom: 20px;
}

.cell {
    width: 35px;
    height: 35px;
}

.cell input {
    width: 100%;
    height: 100%;
    border: 1.5px solid #ccc; /* Make boxes thicker */
    text-align: center;
    font-size: 18px;
    font-weight: bold;
    outline: none;
}

/* Add border after every three columns */
.cell:nth-child(3n+3) {
    border-right: 7px solid black;
}

/* Add border after every three rows */
.cell:nth-child(n+19):nth-child(-n+27),
.cell:nth-child(n+46):nth-child(-n+54),
.cell:nth-child(n+73):nth-child(-n+81) {
    border-bottom: 5px solid black;
}

.controls {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-top: 20px;
}

button, select {
    padding: 10px 10px;
    font-size: 16px;
    cursor: pointer;
    border: none;
    border-radius: 5px;
    background: #007BFF;
    color: white;
    transition: background 0.3s ease;
}

button:hover, select:hover {
    background: #0056b3;
}

select {
    background: #28a745;
}

select:hover {
    background: #218838;
}