There are multiple games to learn CSS – I will update this list as I find more.
CSS Diner
Learn CSS selectors to serve your guests.
FlexBox Defence
A tower defence game with CSS Flexbox.
Flexbox Froggy
Learn Flexbox with a hoppy friend.
CSS Grid Garden
Learn CSS Grid by growing carrots.
Hex Invaders
Destroy invaders to build hex codes.
Bonus!
Here are some additional challenge games to learn other programming concepts