Ask HN: Short and interactive exercises for devs?

The place I work at has a 1 hour time slot every other week for all the devs to meet up remotely which usually has people presenting some topic to teach others.

I want to do something different that is still web dev related, but shouldn't take longer than 30-40 minutes all up including the initial walkthrough.

Skill levels range from one end to the other so I don't want it too challenging, too easy might be okay given such a short time frame.

Some ideas would be ones from codepip like Flexbox Froggy and Grid Garden. (These actually might do the trick)