Thanks! I'm considering writing a follow-up note on the process that went into the typesetting. The original source is a markdown-with-latex format that a tool called pandoc can work with. The style is primarily from tufte.css. The image work is mostly custom, but there are some re-usable approaches. If you're curious:

https://github.com/tylerneylon/math/blob/master/self_repl_fn...

Look at the underline of the words "on github".

The underline doesn't touch the g of github, and furthermore, has a chamfer on it!

Incredible.

I agree - even mobile.

I'm not even interested in the content (sorry!), I just want to look at it. It's seriously beautiful, even on my phone.