清除浮动的方法

<style>
.contain{
    width: 500px;
    /* 给父级容器添加高 */
    height: 500px;   
    border: 1px solid #000;
}
.box{
    width: 300px;
    height: 300px;
    background-color: red;
    float: left;
}
</style>
    

<div class="contain">
<div class="box"></div>
</div>

<style>
.contain{
    width: 500px;
    border: 1px solid #000;
}
.box{
    width: 300px;
    height: 300px;
    background-color: red;
    float: left;
}
.clear{
    clear: both;
}
</style>
    

<div class="contain">
<div class="box"></div>
<div class="clear"></div>
</div>