<div style="position: relative;width:800px;height: 300px;background-color: gainsboro;border:1px solid red;margin: 0 auto">
    <div style="position: absolute;width:100px;height: 100px;bottom: 0;left: 0;background-color: brown">
    </div>
</div>


<div style="position: relative;width:800px;height: 300px;background-color: gainsboro;border:1px solid red;margin: 0 auto"
 
>
    <div style="position: absolute;width:100px;height: 100px;top: 0;right: 0;background-color: brown">
    </div>
</div>


<div style="position: relative;width:800px;height: 300px;background-color: gainsboro;border:1px solid red;margin: 0 auto">
    <div style="position: absolute;width:100px;height: 100px;bottom:0;background-color: brown"
 
>
    </div>
</div>

當需要下層DIV在上層DIV中定位時，上層DIV使用relative,下層DIV使用absolute.配合TOP,LEFT,RIGHT,BOTTOM定位。

DIV(CSS 定位)