Truth is I've been spoiled on that front because I had the luck to work for many year in a company where the CTO was a very talented dude who lived and breathed HTML/CSS since the mid-2000's, and who was quite thoughtful about that kind of stuff, so I had a first-hand experience of a good codebase, mostly by avoiding external dependencies, using the standard browser behavior, and frequently consulting the MDN.
This is why it's a bit disheartening to see so many front-end framework working against the plateform, even even marketing against it, while CSS and browser tooling his so much more enjoyable and powerful than before.