Making Changes to Look of Membership Signup Boxes

Hello!

Thank you for all of your help and hard work! I'm setting up memberships on our website and was curious if there is any way to change the look of the membership signup area. Currently, there are gray boxes surrounding the information, which are slightly off-size. There are no options to change the typeface, nor the "Signup" button itself. How might I go about making these changes, or, at least – where can I find the code to edit these elements? Please see attached for a screenshot of what I currently see on the front page.

Thank you very much.

Atma and the d!a team