#board {
    display: grid;
    grid-template-columns: repeat(3, auto);
    width: 306px;
    margin: 10px auto;
    background-color: #11213a;
}

.cell {
    width: 100px;
    height: 100px;
    border: 2px solid white;
    cursor: pointer;
    line-height: 100px;
    font-size: 60px;
    color: white;
    text-align: center;
}

.header {
    text-align: center;
}