The sidenotes alone are a thing of beauty and wonder. I am very much not sarcastic when I say that.
The vibe is sort of like reading beautiful little booklets, which is wonderful and non-distracting but also not very hypertexty. Their pieces don’t link among each other a ton so far as I’ve read. I wonder if it’s an intentional choice?
Really nice indeed. Looks like it’s the sidenotes from Tufte CSS.