CSS Diner (pick)
https://flukeout.github.io/
Flexbox Froggy
http://flexboxfroggy.com/
Flexbox Defense
http://www.flexboxdefense.com/
Untrusted
https://alexnisnevich.github.io/
hmm CODE HUNT
https://www.microsoft.com/en-us/p/code-hunt-game/9nblggh6d0gs?activetab=pivot:overviewtab
CYBER DOJO
https://www.cyber-dojo.org/
Elevator Saga
http://play.elevatorsaga.com/
Code Wars
https://www.codewars.com/