自动定位div作为一个向下/向上滚动页面

Please see this UI sketch image, I have this div in sidebar (black box) on a certain site and as I scroll down or scroll up, I don't want it to hide...I want it to move itself down as I scroll down and move itself up as I scroll back up so that it never hides out. Can you recommend me some jQuery that can get this done? or something else. Please help, thanks. image, I have this di