main.css

#screen-anterior,#screen{
    width: 11em;
    height: 2em;
    margin-left: 30%;
    text-align: right;
}

.tecla{
    border: 2px solid;
    padding: 3px;
    height: 2em;
    width: 2em;
    padding:0px;
    text-align: center;
}

table{
    margin-left: 30%;
}