#left {
            width: 100px;
            height: 100px;
            background: red;
            float: left;
        }
        #right {
            height: 200px;
            background: yellow;
            overflow:hidden;
        }

<div id="left"></div>
<div id="right"></div>
--
修改:sitepenfan FROM 124.126.195.*
FROM 124.126.195.*