"There's air in my room, it appears transparent. The sky is made of air, it appears blue. Why the difference"

(I will almost certainly do one on quantum mechanics, but that's such a big explanation that I want to do some simpler ones first)

Debates whether to update the sidenote with an explainer on ambitransitive and labile verbs

(Is there something in particular you're referring to? I feel like sticky nav and sidenotes aren't particularly unusual?)

Not unusual, but you used them with taste and restraint, like the rest of your layout and animations. That's something that HN comments like, I think. Notice the distinct lack of "OMG some fancy presentation trick ! Litteraly unviewable!" comments that often happens when an unusual layout is presented (and often with reason; but sometime to a fault).

I guess the main praise your page UI is that it looks, well, like a page. But augmented I guess ?

Personnally I really like the way you used a grid to separate the content from the nav. I like that you used both the left sidebar for nav and for the header number (re-using the same space for multiple purpose feels elegant, because those purpose are secondary to the content, if that makes sense). And I like that the grid anchors your eyes by fencing the different chapters along with the nav. (and now that I mention it, it feels weird that the headings are outside their chapters, but it didn't felt like that upon first reading).

Any other questions give you the same disappointment?

The light "beam" we perceive is the result of infinite circular waves. The points were the light is not are points where they cancel each other out. We had that as part of the school curriculum, do you not have that, or did you forget?