#responsive-form{
    max-width:600px /*-- cambiar esto para conseguir el ancho de la forma deseada --*/;
    margin:0 auto;
        width:100%;
}
.form-row{
    width: 100%;
}
.column-half, .column-full{
    float: left;
    position: relative;
    padding: 0.65rem;
    width:100%;
    -webkit-box-sizing: border-box;
        -moz-box-sizing: border-box;
        box-sizing: border-box;
}

.clearfix:after {
    content: "";
    display: table;
    clear: both;
}

 
/**---------------- Media query ----------------**/
@media only screen and (min-width: 48em) { 
    .column-half{
        width: 50%;
    }
}