Look at this: http://jsfiddle.net/unimous/88uqJ/
<div id="d1">
    <div id="d2">
</div>
</div>
#d1 {
    height: 3000px;
    background-color: red;
}
#d2 {
    background-color: green;
    height: 40px;
    width: 40px;
    position: absolute;
    bottom: 0px;
}
I want to make div d2 appear at the bottom of d1, not the bottom of the screen.
Why position: absolute doesn't work here?
 
    