Have a look at Tailwind. tailwindcss.com
I don't use it but I have been tackling CSS in a very similar way for years. It's easier to understand the concept by checking their site than me trying to explain everything.
It's about building with utility classes and use composition to achieve your goal.
Most people make too high level classes that take care of too many things at the same time.
Then they need to overwrite them, make variants or create new ones. That's when the mess starts :P
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