清除浮动的三种方法和差异

/*空div*/
.clear{clear:both;height:0;overflow:hidden;}

/*after伪类*/

.clearfix:after {
visibility: hidden;
display: block;
font-size: 0;
content: " ";
clear: both;
height: 0;
}
.clearfix{*zoom:1;}

/*overflow:auto */
div{overflow:auto;}