Small Layout Adjustments

Hi There, I need to make some small adjustments to the Layout structure of EasyDiscuss and EasyBlog, so Instead of making a lot of requests here and fill the forum with my issues, I decide to do it by my self, so I am using firebug to find witch classes I need to edit, but I still need one litle help to find the right css file I need to edit. In the attached file I have more details about this.

How Can I find the right CSS file to edit?

With Best Regards
Bruno Alecrim