tr{
    height:  80px;
}
td{
    width: 80px;
    text-align: center;
    font-size: 3em;
}
/* filas impares columnas pares */
tr:nth-child(odd) td:nth-child(even){
    background-color: black;
    color: white;
}
/* filas pares columnas impares */
tr:nth-child(even) td:nth-child(odd){
    background-color: black;
    color: white;
}
h1{
    text-align: center;
    background-color: rgb(129, 126, 126);
    color: rgb(255, 252, 252);
}
form{
    text-align: center;
    font-size: 3em;
    width: auto;
}
table{
    border: double 6px rgb(0, 0, 0);
    margin: auto;
}