Фокус-покус:
<style type="text/css">
* {margin:0; padding:0}
html,body{height:100%}
</style>
<div><div style="position: relative; border: 1px #aaaaaa solid; width: 95%; height: 30px; opacity: 0.5; background:#000000; margin: 0 auto; "><div style="float:left; background:#555555; width: 100px; ">1</div><div style="float:right; background:#999999; width: 20%; ">3</div><div style="background:#777777; " >222</div></div>