Separate projects. Niels Leenheer who made CSS Doom has seen Agustin Capeletto's CSS Quake.

https://bsky.app/profile/html5test.com/post/3mok5febchs2g

And I think both have seen these much older handcrafted css3d engines

- https://pantel.is/projects/css3d/

- https://keithclark.co.uk/labs/css-fps/ (the original)

but quake and doom took it to the next level :)