Really kind of you. Thanks for saying so.

Echoing bobbiechen — it's Squarespace, and this essay was designed as a page, not a blog post, which provided increased flexibility in the design, etc.. It's super robust if you break out of the standard templates.

The site is Squarespace - a few giveaways are the favicon, the <!-- This is Squarespace. --> comment in the head section, and the fact that hitting escape opens the Squarespace login.

This looks pretty different from the usual templates, so I would guess there's a lot of custom code for the visuals.