I think knowing what to ask and where to look represents mastery of CSS.
Understanding the approximate power of things like flexbox and having some aesthetic taste is much of the battle. You have to be willing to get your hands dirty. CSS is almost entirely about art. Figure out which paint brushes and techniques work best for you. There are a lot of viable paths.
No, it has a 3d engine, one that you can happily ignore 99.9999% of the time. CSS has a few gotcha, a few things to got to understand about it (selectors, selector priority and the way content flow depending on absolute / relative positionning), but it is not an impossible language to pick up, far from it.
As the grandparent comment said, don't let the perfect be the enemy of the good.
Understanding the approximate power of things like flexbox and having some aesthetic taste is much of the battle. You have to be willing to get your hands dirty. CSS is almost entirely about art. Figure out which paint brushes and techniques work best for you. There are a lot of viable paths.