两个div左边的固定宽度右边的自动填充的css

<div id="main" style="width:98%;">
<div id="left" style="float:left;width:200px;border:1px solid red;height:100px;">
</div>
<div id="right" style="height:100px;border:1px solid blue;width:auto;margin-left:200px;">
</div>
</div>