Shrink the length of the category bars

[setishock]

See the attachment first.
You'll notice the right end of the category bar extends past the ends of the forum rows. I know it's the thick border causing that but it needs to stay. It's a major part of the illusion of being the light source lighting the tubes the forum rows are sitting in.
So now after exploring and tinkering with the css I've hit a wall and need some help. Which css controls the category bars? I just need to back up the length about 3 or 4 pixels.