clearfix清除浮动

精通CSS(第二版)：

.clear:after {
    content: ".";
    height: 0;
    visibility: none;
    display: block;
    clear: both;
}

bootstrap中清除浮动的方法：

.clearfix {
    *zoom: 1;
}

.clearfix:before, .clearfix:after {
    display: table;
    line-height: 0;
    content:"";
}

.clearfix:after {
    clear: both;
}