First of all, welcome to Webflow!
It is recommended that users share a preview mode of your projects whenever you’re asking for help, so we can try to realize what’s going on with it.
But from what you’ve described, your problem is easily solved by using combo classes. You might be forgetting a tiny detail and that might be the cause of your problems.
Check out this video on combo classes and try to see if you’re not forgetting anything.
Good luck. Let me know if you need anything else.