.one-half-column-left { width:48%; float:left; } .one-half-column-right { width:48%; float:right; } @media only screen and (max-width: 600px) { .one-half-column-left, .one-half-column-right, .one-third-column, .one-third-column-last { float:none; width:100%; margin-right:0; } }