.gomuku {
    width: 400px;
    height: 400px;
    margin: 100px auto 0;
}

.gomuku-inner {
    display: table;
    border-collapse: collapse;
    width: 100%;
    height: 100%;
}

.gomuku-row {
    display: table-row;
}

.gomuku-cell {
    display: table-cell;
    width: 33%;
    height: 33%;
    border: 1px solid #ccc;
    position: relative;
}

.gomuku-cell:hover {
    box-shadow: inset 0 0 2px rgba(0, 0, 0, 0.3);
}

.gomuku-cell-white:before,
.gomuku-cell-black:before {
    font: 48px Arial;
    color: #333;
    top: 20%;
    left: 32%;
    position: absolute;
}

.gomuku-cell-black:before {
    content: '✗';
    font-size: 72px;
}

.gomuku-cell-white:before {
    content: '◯';
    left: 27px;
    font-size: 58px;
}