Wikitable class "collapsible"

I'm trying to build a template with the "collapsible" class (just copy & 
pasting from Wikipedia) and I don't get it to collapse.
So, I figured I was missing something from either Common.css or 
Monobook.css. I copied them over in their entirety and it still doesn't 
work (yes, I cleared my cache, etc.)

So, what am I missing?
I'm running Mediawiki 1.10

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Kimon Andreou
Information Technology
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