z-indexing problems

[anarchist]

I have a navigation system that I'm implimenting similar to outlooks outlook bar

I'm having trouble with my z-indexes for when I scroll my groups, when I say scoll I sctually slide the contents rather than scroll them

I'll try demonstrate in the diagram below its a side view to show the layering

____ = a group

this is the normal start of view

 
    ____
  ____
____

afer scrolling the top group

 
 ____
  ____
____

the problem I'm having is I have buttons at the top of each group to select them and when I scroll the top group the items go below the top button but go over the top of the lower buttons

the structure I'm using for groups is

 
group
   |
   |--Button
   |--Scrollable items
           |
           |--Items

can any one help?

[anarchist]

I'm trying to use clip to cut the top off the group when its scrolled, this seems to have the right effect but, I now have a javascript problem with my maths