我们经常用伪类来清除浮动，比如这样
.clearfix:after { content: ""; display: block; clear: both; height: 0;}.clearfix { *zoom: 1; }//hack IE6我们来看一下样例：
<!DOCTYPE html><html><head> <title></title> <style> *{ padding: 0px ; margin: 0px ; } .block{ width: 100px ; height: 100px ; float: left ; margin:10px; border: solid 1px ; } .clearfix:after{ content: "" ; display: block; clear: both ; } </style></head><body><div class="clearfix"> <div class="block"></div> <div class="block"></div> </div> <div class="block"></div> <div class="block"></div></body></html> 本来四个格子是同行排列的，清除了浮动后就在清除浮动的地方换行了。
注意一定要是在父类添加清除浮动的clearfix类，如果不加在父类上是没有用的。我个人的理解是这样的，像before和after这样的伪类其实就是在元素内部的前面或后面添加一个元素，这样效果是一样的
<!DOCTYPE html><html><head> <title></title> <style> *{ padding: 0px ; margin: 0px ; } .block{ width: 100px ; height: 100px ; float: left ; margin:10px; border: solid 1px ; } .clear{ clear: both; } </style></head><body><div> <div class="block"></div> <div class="block"></div> <div class="clear"></div> </div> <div class="block"></div> <div class="block"></div></body></html> 但注意下面这样是不行的
<body> <div class="block"></div> <div class="block clearfix"></div> <div class="block"></div> <div class="block"></div></body>
还可以用overflow来清除浮动
<!DOCTYPE html><html><head> <title></title> <style> *{ padding: 0px ; margin: 0px ; } .block{ width: 100px ; height: 100px ; float: left ; margin:10px; border: solid 1px ; } .clear{ overflow: hidden; } </style></head><body><div class="clear"> <div class="block"></div> <div class="block"></div> </div> <div class="block"></div> <div class="block"></div></body></html>
清除浮动的另外一个原因就是要把浮动元素的父元素撑开，为什么用overflow能清除浮动我查到了以下这段话:是因为overflow除了(visible)会重新给他里面的元素建立块级格式化(block formatting context)floats, position absolute, inline-block, table-cell和table-caption都不是块级样式，所以才会用到clear来控制浮动overflow也可以清除浮动是因为当在父级元素设置overflow时候，除了visible，就是只有auto, hidden或者scroll时候，也会建立新的块级格式给他的子元素, 从而起到清楚浮动效果具体信息可以在这里看虽然clear是旧的方式，但还是推荐用clear来做，有些情况会比overflow处理的要好.
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