Tell that to a decent number of people I have worked with over the past 20 years. In fact, I know people to this day who have been writing CSS for decades who don't really know fundamental things like specificity, inheritance, or the cascade. Pattern matching into the sunset, not a single fundamental piece of CSS specifications ever internalized, still getting paid (its okay).
https://www.w3.org/Style/CSS/specs.en.html
You can read this and know most things about CSS. For a bit anyway. You'll forget things you don't use. You might remember them again one day.