My final conclusion about CSS is - program the damn machine.
What I mean by this is STOP every single type of abstraction/library/programming layer for CSS - nothing gets it right, everything causes a problem.
The ONLY way to deal with CSS is program it directly in the way the docs say, never anything else.
There's nothing wrong with using Bootstrap or whatever, and I definitely use JavaScript to program CSS. What I am saying is - no abstractions - no "better way" - no trying to turn CSS into something it isn't via whatever your new abstraction is that can be added to the N other abstractions that other people have made over the years.
Program the damn machine.
For me nothing beats plain old classes and an external css file. For PWAs I just use lit css within the element, again with classes and plain css. If things cause problems, just figure out why and fix the classes.
This is exactly how I feel. Learn how to write CSS! Like you would do with any language!
CSS suffers from one of its original design tenants in that it's very easy to throw some shit at the wall and kind of get it working without fully understanding it. This is especially true for people who have dabbled in it from time to time in their career when absolutely needed. It's rare to see someone sit down and learn it from first principles. It doesn't take long and knowing the basic theory goes a long ways!