SL 360 - Flip cards interaction using JavaScript and CSS

Hi,

I'm learning JavaScript specifically to be able to extend interactions in Storyline. I want to create a flip-card interaction to reveal more information and I have a concept on Codepen.io using the concept. But now I'm trying to figure out how to apply in an SL slide. It relies on CSS classes and I'm not sure how to add a CSS class in SL.

Here's the Codepen.io sample functionality: https://codepen.io/kthayer-git/pen/KKVqLyo?editors=0010

Thanks for any suggestions/tips.