<!DOCTYPE HTML> <style type="text/css"> html, body { margin: 0; padding: 0; border: none; } </style> <div style="margin: 100px; height: 400px; width: 400px; display: -moz-box; -moz-box-orient: horizontal"> <div style="width: 200px; box-shadow: 0 0 14px blue">A</div> <div style="width: 100px"></div> <div style="-moz-box-flex: 1; box-shadow: 0 0 14px blue">B</div> </div>