There is a way to use a custom CSS file when creating a website on CampusGroups.
Manage your group.
Click on the "Website" tab (in the manage toolbar).
Click on "Options" (last tab in the website menu).
4. Scroll down to the "CSS" session and click on the "Edit CSS" button.
5. You will be able to add/edit your CSS there. Click on the "Save" button to finish.