Neat! I would be interested to know how performance differs between CSS 3D transforms vs something like threejs that renders onto a canvas node for this specific kind of directionally-lit voxel scene.

I would imagine that CSS transforms are heavily optimized for in browsers and the much simplier kind of rendering you're doing here probably cuts out some stuff webgl would be doing, but there is the overhead of DOM updating that might have some sort of impact. However it's hard to beat cracking open dev tools and just hoving over the quad you want to peek at!