Great mod Clyde!

I have a dumb question.
I need to adjust the way the sidebox looks on my site: http://adriftwood.com
I want it to blend in and look like the other sideboxes.

I thought I knew how to do it, but apparently I don't. LOL
Everytime I try to change the background color, it's not solid...it's like it changes behind part of it, but not the whole box.

Thanks!