Oh, wow. When this came up before, I don't know if I looked at the DOM, because I assumed you would do this type of thing by drawing pixels on a Canvas. It's actually made of HTML elements? That's impressive.
But large blobs drawing to `canvas` aren't anything new at this point. The part that impressed me is doing it the simple way, using what the browser already provides, and getting it to work this well.
As a reference, here is a browser-adapted version of the https://cuis.st/ Smalltalk environment, which does its own rendering onto a canvas:
https://github.com/nmingotti/The-Cuis-CookBook/wiki/Run-Cuis...
Working within the confines of HTML is way more impressive to me.