Hi bpeikes
Can you elaborate on what you mean by "interactive filters"?
Generally speaking, you can use the REST API to get info about your themes and the currently used themes by using the "/themes/current" end point.
Assuming that you need it to be dynamic by a user group or something similar then you'll need to do some JS work to load the current theme and set your CSS accordingly. Keep in mind that this should be an async task so it can get a bit complicated and you should test your work with a slow vs fast network and computing resources.
If it doesn't need to be dynamic and you simply want to avoid doing manual styling to all your blox widgets that you should move the styling into a custom plugin that would apply the styling in a more generic way so you won't need to apply it everytime.
Another option is to utilize our widget script manger plugin to easily inject the scripts and manage them in a centralized place BUT this might be an overkill as this is a commercial option...
Feel free to reach out of you have further questions, we're always happy to help (: