Adjust column width

I want to reduce the amount of space between columns, i tried the following, it looks good on a PC but it breaks the horizontal view on mobile devices–

.su-row .su-column-size-1-3 {
width: 32%;
}
.su-row .su-column {
margin: 0px 0 0 2%;
}
.su-row {
margin-bottom: 1em;
}