Membership registration page

Hello,

I new to using Wordpress Membership and I've successfully added the sign up and registration pages but the formatting is all over the place on the sign up page and the text is too small on the page where you select your membership. Could someone help me out? Changing theme isn't an option so I need to edit the CSS.

http://www.soundscrew.net/live/registration-page

Thanks for all your help.