.container {
    border: 1px solid black;
    background-color: lightsteelblue;
    height: 330px;
    width: 330px;
    display: table-cell;
    vertical-align: middle;
    text-align: center;
}
div div {
    border: 5px solid steelblue;
    height: 306px;
    width: 306px;
    display: inline-block;
}

div div div{
    border: 1px solid black;
    font: 90px arial;
    color: lightslategrey;
    width: 100px;
    height: 100px;
    float: left;
}

.X {
    color: red;
}

.O {
    color: blue;
}

.button {
    border: 1px solid black;
    background-color:lightcoral;
    color: red;
    border-radius: 4px;
    font: 20px arial;
    margin-top:5px;
    padding-top: 5px;
    display:block;
    height: 30px;
    width: 120px;
}