//只适用于右边的比左边的高度长
<style>
.parent_elem {
overflow: hidden; position: relative;}
.right { float: right; width: 92%; }
.left { float: left;width: 8%; }
.left_pos {position: absolute;width: 100%;
height: 100%;}
</style>
<div class="parent_elem">
<div class="right">右边的比左边的长右边的比左边的长右边的比左边的长右边的比左边的长右边的比左边的长</div>
<div class="left">
<div class="left_pos">左边的短</div>
</div>
</div>