如何将元素放置在具有高度和溢出的div的底部：auto

Here is my situation, I have a div which has height:400px and overflow:auto to get scrolled when the content is longer than 400px. inside this div I have 2 divs. A normal one with unkown height and another with absolute positioning which in anchored to bottom:0px;Here is my situation, I have a div which has he