<div style="width: 100%; display: table;"> <div style="display: table-row"> <div style="width: 600px; display: table-cell;"> Left </div> <div style="display: table-cell;"> Right </div> </div> </div>
<div style="width: 100%; overflow: hidden;"> <div style="width: 600px; float: left;"> Left </div> <div style="margin-left: 620px;"> Right </div> </div>