CSS
CSS Font Shorthand Property Cheat Sheet
Learn CSS Layout - a favorite of Leon's
Getting to Know CSS - by Shay Howe, really good (homework)
A Complete Guide to Flexbox - I like this one a lot
Flexbox Froggy - this is good (homework)
Flexbox Zombies - gamified flexbox learning tool
Complete CSS Grid Tutorial with Cheat Sheet - this is very good!
Kevin Powell on YouTube - a lot of folx have recommended his video