I don't think learning something necessarily mean knowing lots of names/properties by heart. You should however have a good idea of what grid and flexbox can do for you and when to use them I think.

I personally have a hard time differentiating between properties such as justify-content / align-content / align-items / justify-items / justify-self and so on. To me those are just random words. Perhaps because English is not my first language, I don't know.

I really think it makes a huge difference to see a small icon describing what properties have been set and to see the difference by hover instead of just reading/editing raw CSS.

I've visited https://css-tricks.com/snippets/css/complete-guide-grid/ and https://css-tricks.com/snippets/css/a-guide-to-flexbox/ countless of times. Some of the stuff just does not seem to stick tbh, especially if you have been working on something not-CSS related for some time.

I'm sure some people just remembers everything, but i'm not one of them :)