CSS

The MDN docs are the gold standard. You can learn everything you need to know through the MDN docs alone.

The CSS specifications are surprisingly user-friendly! I learned a ton reading the Flexbox spec.

Rachel Andrew wrote a terrific blog post, How to Learn CSS.

The CSS Tricks Almanac is a great resource for digging into particular properties.

Flexbox Zombies is a great way to learn the rules of CSS Flexbox.

This blog includes lots of CSS tutorials, including many lessons plucked straight out of the course!

The Rules of Margin Collapse

What the Heck, z-index??

An Interactive Guide to CSS Transitions

Full-Bleed Layout using CSS Grid

CSS Variables for React Devs