Making shapes with CSS will never fail to impress me and I just spotted this great resource by Temani Afif that has a ton of examples. You’ve got the basics, like squares, triangles, and circles but then the more wild examples like ribbons and grid lines. Great stuff.
Also, completely unrelated to all this, but I had a lot of fun scrolling through Temani’s work on Codepen. Especially this trippy, 3d parallax effect and this, the ultimate CSS shape of them all: a CSS-only Goku.