I learned them the hard way by designing reflow typography layouts in the late 90s and early 00's, mixed with interactive elements; and later thinking out whole sites with layouts that weren't reliant on a particular DOM or browser. It's a bit stunning to me that Google taught any of these principles at any point beyond eliminating all the art. Which to me was the beautiful part of the early web.

I have literally no idea what people are learning now in academies before being set loose to do front-end work, but obviously it's mediated through so many libraries that they haven't had much time to consider what's going on behind low-level user interactions and load sequences.