The best way to learn CSS has always been a mystery to me. There's lots of tutorials, and on the surface, CSS seems deceptively simple. But when you get into the weeds, you realize that it can be extremely complex.
And while you don't need to know everything there is to know about CSS, there's a few concepts that are so widely used (in close to every website in existence), that it really pays off to learn them well. Those are Flexbox and CSS Grid, the modern CSS layout tools.
I remember when I was just learning CSS, Flexbox and Grid were mysteries to me. Getting the exact layout I wanted was more of a guessing game than anything else. Until I discovered two exceptional resources to really solidify the concepts and innerworkings of the properties, specifically:
These are awesome visual games with multiple levels to teach you Flexbox and Grid through a step-by-step process. I definitely recommend checking them out, even if you think you already know Flex and Grid. You just might get a better understanding or learn something you didn't already know!