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Other interesting games for learning CSS,

https://cssgridgarden.com/ (basically Froggy for Grid)

https://cssbattle.dev/ (a platform for doing various challenges, huge community)

https://flukeout.github.io/ (learn about CSS selectors)

Not sure if it's still a fully free thing but I also remember having a go at https://flexboxzombies.com/ in the past.

It's still free!

Created an account and attempted to start in Firefox: got some kind of endless loading animation.

Opened an Edge window, attempted to sign in: had a long wait followed by an error message about a network failure.

I found flexbox froggy lacking of some extra details and was able to fill the gap here,