1. overfloat: hidden
css代码：
<style type="text/css">
#box {
border: 10px solid #616161;
overflow: hidden; /* overflow: hidden add to parent can clear float*/
}
#content {
float: right;
width: 600px;
height: 600px;
border: 5px solid #400000;
width: 600px;
}
</style>
HTML，div代码：
<div id="box">
<div id="content"></div>
</div>
2. clear: both
css代码：
<style type="text/css">
#box {
border: 10px solid #616161;
}
#content {
float: right;
width: 600px;
height: 600px;
border: 5px solid #400000;
width: 600px;
}
.clearb {
clear: both; /*clear: both add to the last sibling can clear float*/
}
</style>
HTML，div代码：
<div id="box">
<div id="content"></div>
<div class="clearb"></div>
</div>
子类div不在父类div中，需清楚浮动， 清除浮动的两种方法
原文：http://www.cnblogs.com/Super0206/p/4970090.html