.clearfix {
    zoom: 1; /*IE低版本浏览器不支持after伪类所以要加这一句*/
    &:after {
        height: 0;
        content: " ";
        display: block;
        overflow: hidden;
        clear: both;
    }
}
.left {
    float: left;
}
.right {
    float: right;
}

<div class="clearfix">
    <div class="left"></div>
    <div class="right"></div>
</div>