> I know like 10-15 different languages, and CSS is by far the hardest to read and understand.

CSS is hard to know, even if you know 15 languages.

I can understand many programming languages and write in a subset of many of their features, but I wouldn't claim to know them. That would require a monumental amount of day to day effort, in my opinion (see https://en.wikipedia.org/wiki/Illusion_of_explanatory_depth).

To me, the best way to understand CSS is to evaluate it after rendering, and I have been writing it for decades.