1234567891011121314/* .clearfix::before 作用:解决外边距塌陷问题 外边距塌陷:父子标签,都是块级,子级加margin会影响父级的位置*//* 清除浮动 */.clearfix::before,.clearfix::after{ content: ''; display: table;}/* 真正清除浮动的标签 */.clearfix::after{ clear: both;}