.cell {
    font-size: 5em;
    display: inline;
    border: 3px solid grey;
}

.cell.cross:before {
    content: "\2718";
}

.cell.circle:before {
    content: "\25cb";
}

.row {
    display: flex;
    flex-direction: row;

    width: 400px;
}

.cell {
    font-size: 5em;
    border: 3px solid grey;
    
    width: 100px;
    height: 100px;
    text-align: center;
}

.cell.cross:before {
    content: "\2718";
}

.cell.circle:before {
    content: "\25cb";
}

Use flexbox to simplify the layout
Use flexbox to simplify the layout
