Change Categories Block appearance

Hi all

Just wondering how i can put a border round the categories block on the basic theme to make it look more in line with the other blocks?

I have tried changing the Wrapper from the block settings, but this makes the small arrow icon out of line…?

I just cant seem to get where it pulls the formatting from?

Thanks, Anthony

CSS, sir. This is in the CSS.

/skins/[YOUR SITE SKIN]/customers/styles.css (or styles.base.css).