body {
    font-family: Arial, sans-serif;
    text-align: center;
    background: #f4f4f4;
}
h1 {
    color: #333;
}
#sudoku-board {
    display: grid;
    grid-template-columns: repeat(9, 40px);
    grid-template-rows: repeat(9, 40px);
    gap: 1px;
    margin: 20px auto;
    border: 2px solid #333;
    width: fit-content;
}
.cell {
    width: 40px;
    height: 40px;
    text-align: center;
    font-size: 20px;
    border: 1px solid #ddd;
    background: #fff;
}
.cell input {
    width: 100%;
    height: 100%;
    border: none;
    text-align: center;
    font-size: 18px;
    outline: none;
}
button {
    padding: 10px 20px;
    font-size: 18px;
    cursor: pointer;
}