<style>
.box{height:500px;width:1000px;margin:50px auto 0px;border:1px solid red;}
.left{float:left;height:400px;width:300px;border:1px dashed blue;}
.right{height:400px;width:500px;margin-left:100px;background:green;}
</style>
<div class="box">
<div class="left"></div>
<div class="right"></div>
</div>
为什么.right{margin-left:100px;}是相对于div.box的而不是相对于div.left的?