body{
    font-family: Arial, Helvetica, sans-serif;
}

table{
    border: 2px solid midnightblue;
    margin: auto;
    border-spacing: 0;
}


table tr td{
    border: 1px solid midnightblue;    
    height: 50px;
    width: 50px;
    text-align: center;
    font-size: 2em;
}

 table tr input{
    border: 0px;    
    height: 50px;
    width: 50px;
    text-align: center;
    font-size: 1em;
 }

 .centrar{
    text-align: center;
    font-size: 3em;
 }
 .fondo{
    background-color: rgb(180, 205, 228);
 }

 .estaba{
    color: red;
 }