But sometimes, that advice actually equates to "don't drive the minivan in your garage. Go out and buy a bicycle."

By the way, do you have any suggestions for tutorials that teach someone a mental model for how CSS/HTML layout works? In particular, I'm looking for a mental model that I can apply consistently and which doesn't feel like I'm playing whack-a-mole. So far I've found that with flexbox, but I'm still finding myself in situations where I need to work with existing block/inline/inline-block code.

Very sadly, I don't. Beyond the Box Model (and the basic notion of "cascading"), there seem to be very few mental models, as such, out there; if anything, people tend to learn through a collection of experiences (many of them negative, at the outset).

Not that there aren't important concepts to understand. Just that the quirks and exceptions tend to rise up from the mists, and -- just when you thought you got a handle on some particular area of functionality -- overwhelm the nice, tidy, conceptual aspects.

Which is why it has proved to be by far the hardest programming environment I've ever hard to learn.

Reading the source of popular open source frameworks is a great way to get a sense of how to write maintainable, reusable CSS. Oftentimes it's not actually too confusing behind the scenes because CSS logic is relatively straightforward to begin with.

Other than that, the hard knock school of life is my primary instructor. There's no "Code Complete" for your stylesheets (at least not one that I've found).