The Advanced Development section covers a variety of technical implementations and snippets that you can use to enhance your IFrame experience.
Here is a link to zingfit's IFrame design guide for Developers:
Please note: the CSS suggestions may or may not work 100% of the time. It's possible another CSS element is trumping your CSS which will require troubleshooting on the studio's end.
Zingfit support does not troubleshoot this guide on studio accounts.