CSS如何解决自适应高度问题？

CSS代码：
* { margin:0; padding:0; list-style:none;}
body { font-family:"微软雅黑", Arial, "宋体", serif; font-size:12px; color:#000000; background:#ECECEA;}
......
#content_main { }
#content_title { display:none; }
#content_body { width:980px; margin:0 auto; background:#FFFFFF; padding-bottom:20px; }
#content_bottom { display:none; }
#left { width:235px; height:95px; float:left;}
#right { width:765px; float:left;}

HTML代码：
<div id="content_main">
  <div id="content_title"></div>
  <div id="content_body">
     <div id="left"></div>
     <div id="right"></div>
  </div>
  <div id="content_bottom"></div>
</div>