Besides its clean and simple appearance, I appreciate the fact that it uses very clean and modern CSS with rules like @layer or @import. This demonstrates that it is possible to use only CSS (without SASS or other preprocessors) to maintain well-structured code [1].

Another interesting part is the license. I had never considered Disallowed Uses before [2].

[1] https://github.com/cferdinandi/kelp/blob/main/css/kelp.css

[2] https://github.com/cferdinandi/kelp/blob/main/LICENSE.md