清除浮动的四种方法

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

.clearfix:before .clearfix:after {
                content:"";
                display:table;
                }
.clearfix:after {
                clear:both;
                }
.clearfix {
                *zoom:1;
                }