左侧div自适应右侧div高度

 1 <div class="wrap first">
 2   <aside>
 3     aside
 4   </aside>
 5   <section>
 6     a<br/>
 7     a<br/>
 8     a<br/>
 9     a<br/>
10     a<br/>
11     a<br/>
12     a<br/>
13     a<br/>
14     a<br/>
15   </section>
16 </div>

 1 .first{
 2     position: relative;
 3     border: 1px solid black;
 4   }
 5   aside{
 6     width: 20%;
 7     height: 100%;
 8     border-right: 1px solid black;
 9     position: absolute;
10   }
11   section{
12     width: 70%;
13     margin-left: 28%;
14     height: auto;
15   }