table.Morpion {
    margin: 20px auto;
    border-collapse: collapse;
}

table.Morpion td {
    text-align: center;
    width: 100px;
    height: 100px;
    border: 3px solid black;
    margin: auto;
}

table.Morpion td.vide {
    background: white;
}

table.Morpion td.croix {
    background: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100"><line x1="10" y1="10" x2="90" y2="90" stroke="red" stroke-width="10" /><line x1="90" y1="10" x2="10" y2="90" stroke="red" stroke-width="10" /></svg>') no-repeat center;
}

table.Morpion td.cercle {
    background: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100"><circle cx="50" cy="50" r="40" fill="transparent" stroke="green" stroke-width="10"/></svg>') no-repeat;

}

table.Morpion td.gras {
    border: red;
    outline: 10px solid red;
    outline-offset: -5px;
}