<div id="left">left</div>
<div id="right">right</div>

<style>
#left{
width: 200px;
line-height:50px;
background:green;
float:left;
text-align:center;

}
#right{
margin-left:200px;
line-height:50px;
background:red;
text-align:center;
}
</style>