如何动态更改div的高度以匹配包含它的div的大小

I got div1 and div2 with div2 containing div1 (and some other elements). I want to dynamically change the height of div1 to match the height of div2(- the height of the other elements) whenever div1 exceeds that height. The reason I don't just set div1's height outright is because div2's size isn't fixed and I want the horizontal scroll bar from div1 to stick to the bottom of its content and not to the bottom of div2.I got div1 and div2 with div2 containing div1 (