<div class="m-box">
<div class="left">左</div>
<div class="right">右</div>
</div>
html,body{margin:0; padding: 0;}
.m-box .left,.m-box .right { height: 200px; line-height:200px; text-align:center; }
.m-box .left{float:left; width:200px; background-color:#ccc; }
.m-box .right{margin-left:210px; background-color:#666;}