HTML代码如下：

<div style="border: 1px red solid; width: 400px; height: 100px;margin-bottom: 10px;" class="claerfix">

123

</div>

<div style="border: 1px red solid; width: 400px; height: 100px;margin-top: 10px; " class="claerfix">

123

</div>

CSS代码如下：

.claerfix:before,.clearfix:after{

content: " ";

display: table;

}

.claerfix:after{

clear:both;

}

效果如下：