Someone made 512 icons with pure CSS (cssicon.space)

These icons are released under CC0, meaning that it is as close to public domain as you can get in many territories.

I never understood why people prefer abusing CSS to create icons when SVG is a much more suitable candidate for this kind of job. And in many cases they can be smaller in file size too.

This is a project of Wenting Zhang and she also gave a talk about this at dotCSS 2016: https://www.youtube.com/watch?v=Y0_FMCji3iE

She also has a video where she explains her project: https://www.youtube.com/watch?v=ZOiRwXOIsx4

I don't understand how this works