body {
    font-family: Arial, sans-serif;
    text-align: center;
}

#board {
    display: grid;
    /* 19 columns, each 28px wide*/
    grid-template-columns: repeat(19, 28px);
    grid-template-rows: repeat(19, 28px);
    gap: 2px;
    justify-content: center;
    margin: 20px auto;
}

#board button {
    width: 28px;
    height: 28px;
    padding: 0;
    border: 1px solid #999;
    background-color: #deb887; /* wood-ish board color */
    cursor: pointer;
    border-radius: 50%;
}

#board button.red {
    background-color: #d9362b;
    border-color: #7a1f18;
}

#board button.yellow {
    background-color: #f4d03f;
    border-color: #a08000;
}

/* once a spot is taken, show a "not allowed" cursor instead of a pointer */
#board button.red,
#board button.yellow {
    cursor: not-allowed;
}