.span_3_of_3 {
    width: 100%
}

.span_2_of_3 {
    width: 66.13%
}

.span_1_of_3 {
    width: 32.26%
}

.span_1_of_3:nth-child(3n+1) {
    clear: both;
    margin-left: 0;
}

@media only screen and (max-width: 768px) {
    .span_1_of_3, .span_2_of_3, .span_3_of_3 {
        width: 100%
    }
}