You read that right. A game. It's found here: https://serviceworkies.com/
The developers (Google developers) teach the key concepts of progressive Web apps (PWAs) in a cool way as a game.
I've just completed all the levels and defeated a giant snail, beetle and some other crazy beasts while simultaneously learning about cache, service workers and the life cycle of service workers.
You can't simply copy and paste code and at the end of each stage there is a challenge to try and remember all the code from the previous lessons. I loved it and I'm sure you will!
Go to https://serviceworkies.com/ and sign in to learn how to work with service workers to make your website work offline, feel like a native app and have fun along the way!