Am I missing something, or is Webflow fundamentally not allow you to apply multiple classes to an element without trying to generate thousands of unnecessary combo classes?
Edit: shortened the rant
Hi Michael!
You’ll have to create separately the classes.
First the button. then the second one let’s say alert with only the changes.
That will create ‘global classes’ you’ll be able to add to any element (that was created before they did).
I’m bad at explaining things so I made a video
I hope this helps 
Global styles & a bit of specificity recording
Aha, ok so it does work, but looks like the functionality is unreliable at best. Too easily to accidentally make a combo class without any ability to change it to a global class short of deleting it, removing it from the style manager, then recreating it from scratch and hoping it doesn’t accidentally become a combo class again.
Appears like the majority of the issue comes down to how poorly the entire Style Manager feature functions - where it offers absolutely no ability to actually manage styles beyond renaming them …
But then a fundamental question still stands, whenever I apply a global style to some element which already has a style, it creates a new combo class. So the moment you’re 5 minutes into a project, you already have a hundred duplicate classes cluttering up the Style Manager making it even more useless.
One solution is to create a Style Guide page, where you create all your utility classes in isolation. Then when you work on the pages facing the visitors, just adding classes through Custom attributes class="the list of all your classes". This has some downsides, as the properties of those classes won’t appear in the Styles panel.
I guess Webflow have decided to go with the way of constant creation of combo-classes, as otherwise might have been tricky teaching people about cascading and inheritance.