I understand where to put classes, I don't know, where to define them. It is probably trivial, but I'm stuck here. I've tried some classes I already use globally, but no success.
I'm an Oxygen user, if it's relevant.
The classes are used to style the custom fields in the backend or the frontend form in the frontend. If you want to style the field value on the frontend, please add the HTML tags with classes to style them. Or contact Oxygen support to ask for help with this case.
For now I need to style custom fields in the backend. Where or how would you define test-class-1 and test-class-2 as is on your screenshot? Which css stylesheet does it use? Is the problem Oxy-related?