Hi,
There are style fields in an addon for a CSS class and Custom CSS. I've yet to get these to actually work so I typically add the CSS to my custom.css file. However, it would be very helpful if I could get them to work.
Please see this screenrecording for explanation:
https://www.loom.com/share/a3a544507c974e4c85b13f5f3ddb9107
It's the first section on this page that I am referring to in the video:
https://mavendesignstudio-demo.com/moa/sandbox