This is neat, and reminds me of <a href="http://www.themaninblue.com/experiment/Cubescape/new.php" rel="nofollow">http://www.themaninblue.com/experiment/Cubescape/new.php</a> circa 2010. Very clever uses of css.
Cute but just in case this is an extremely inefficient way to display this kind of data both inefficient in speed and in memory. It also fails in firefox because the algorithms for sorting 3D css are not specified. Or if they've have been finally firefox hasn't implemented them. And, even if they have been specified that just adds more crazy work the browser would have to do what a canvas 2d or webgl solution would not
Cute, but perhaps incomplete? If I leave the POV right where it is, and if I plan my artwork correctly, maybe I can build something. But if after I start, I decide I need to hang a voxel off the other side of an existing voxel, I spin the view around, the voxels have no back side that I can select to attach against.