table.calculette, table.calculette td {
    border:1px solid black;
    border-radius: 5px;
    background-color:#444;
    margin:50px auto;
}

table.calculette td[colspan] {
    text-align:right;
    padding-right:0.3em;
    background-color:#9f9;
}

table.calculette td:not([colspan]) {
    text-align: center;
    width:3em;
    background-color:#eee;
    cursor:pointer;
}