clearfix

/* new clearfix */
.clearfix:after {
visibility: hidden;
display: block;
font-size: 0;
content: " ";
clear: both;
height: 0;
}
* html .clearfix             { zoom: 1; } /* IE6 */
*:first-child+html .clearfix { zoom: 1; } /* IE7 */

You may combine the hack for IE6 and IE7:

.clearfix{*zoom:1;}

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If you don‘t want additional tags, use bellow:

.group:after,
#content:after,
#sidebar:after,
#some .other .thing:after
{
visibility: hidden;
display: block;
font-size: 0;
content: " ";
clear: both;
height: 0;
zoom:1;
}

clearfix

原文：http://www.cnblogs.com/ipup/p/4351421.html