[benhoyt]

I just checked one of the best "online-first" technical books I can think of, "Crafting Interpreters" by Bob Nystrom, because it uses side notes heavily. What it does when the screen width is narrow (like on a phone) is move the side notes to the main flow, but in a smaller font size and separated with horizontal lines to set them off.

It does break up the flow a little bit (which is why they're side notes in the first place), but at least they're clear and obvious. And this book's side notes are often quirky and interesting -- definitely worth reading!

Example: https://craftinginterpreters.com/the-lox-language.html