You should be looking at the "#Partition_Left_Wrapper" id in the CSS code. It's the third one down.
I am following a tutorial, but the guy does not use a external stylesheet. Not sure if this affects css3 syntax/layout (relatively new here), but I can't seem to access the child block from the parent:
Using an external stylesheet or style should make no discernible difference, unless there are naming conflicts, in which case it could - although the order in which you add files or style tags would be important in this case.
Generally this is the priority...
Inline style (inside HTML tag, e.g. span, p, li etc)
Style tags in head (<style>)
However, as mentioned if the CSS file is placed after the style tags, then elements may be overridden.
Well, the problem is that DIV is a empty box, you should put something can make it like a real box, cuz when you try to use a mouse to click or hover there should have a button or other can let you notice on it.
Else you can't really know where can touch or click it when you try to hover or click it with a event.