There's an air of "I am very smart" about the guy who claims to have memorized the entirety of CSS in a weekend.
Who said that?
The grandparent post. After a weekend of CSS you don't even know what you don't know. The complexity isn't the syntax, its the interactions between all of the elements.
The grandparent post said nothing about memorizing.
Know enough to humbly know that I know far from everything or know just enough to be dangerous?