Incredible. I was so skeptical that I went in on the neckruff and from there to a lacetop, it's really all generated based on background-image but without using images but gradients of specific colors, as well as box-shadows and the like.
Similar problems on my MBP, actually – just sans crashed tab. Zooming in and scrolling around on Chrome and Safari cause the divs to rerender (repaint?) and often not all of them even do! E.g. Chrome: https://imgur.com/a/VWCAL9G
I don't think any on the first page are interactive. There might be a few on the next page of it (I only found one where a pen changes color on hover).
This immediately brought "A Single Div"[0] to mind, which stood as the coolest CSS demo I'd seen for... 11 years!
This one takes the cake. I'll be pouring over it. Thanks!
[0]: https://a.singlediv.com/