Style: Rolling over a button causes resource widths to change

1. Go here: http://current.dev.curriki.org/xwiki/bin/view/Coll_NROCMath/Algebra1AFromNROCUnit4Intro?bc=;Coll_jrhimath.Default
2. Roll over any button

Bug
The resource box changes width and the area repositions itself.

Feel free to try other resources in the collection above to see the issue.