.grid { 
    margin: 1em auto; 
    border-collapse: collapse; 
}
.grid td {
    cursor: pointer;
    width: 30px; height: 30px;
    border: 1px solid #ccc;
    text-align: center;
    font-family: sans-serif; font-size: 13px;
}
.grid td.clicked {
    background-color: yellow;
    font-weight: bold; color: red;
}