It looks like it has style from one of the older dcarter skins.
What I would do is swap out the styletreeview.css file with one from another skin, maybe try a few different ones until you find one you like. If you don't find one you like in the currently shipped skins you could also try the extra skins download. Whenever you swap out the file go to Administration > Advanced Tools > Design Tools > Cache Tool and click the button to reset the skin guid so it reloads the new css.
Hope that helps,