All they have to do is remove "p {max-width: 28rem;}" and the website becomes beautiful. The text fills the entire width of the screen, and the font scales with the screen size (though they should dial it back a bit, or have a different scaling ramp). It's like reading an actual document, and how the web should be. Bonus points, it's ridiculously "responsive" for small screen sizes.

Yes, I know they got it kinda "wrong", but they're arguably going in the right direction here. I'd give the author points for trying something out of the box, and also for "sticking it" to the monstrosity that Bootstrap started many years ago.