I just tried with one of my sites and it seems to work as expected. In my case, I tried it on a course summary:
If the styles are working properly on the login screen, I don't see a reason why they wouldn't work for any other screens or with any of your custom classes. So I think your only option is to use the developer inspector to see what's going on, but this should work.
Make sure to purge all caches as well, to make sure that you're using the latest files (both from the Moodle site and the app).