使用Contentdiv作为页面的容器。

 .sidebar {
     position: fixed;
     width: 200px;
     height: 400px;
     background: #000;
 }
 .content {
     margin-left: 200px;
     height: 500px;
     width: auto;
     position: relative;
     background: #f00;
     overflow: auto;
     z-index: 1;
 }
 .info {
     width: 1440px;
     height: 300px;
     position: relative;
     background: #f55;
 }

<div class="sidebar"></div>
<div class="content">
    <div class="info"></div>
</div>

http：//jsfiddle.net/djw 28/jz52u/

例子：

@media (min-width:600px) {
   .sidebar {
     width: 250px;
   }
   .content {
     margin-left: 250px;
   }
 }