It's also nearly 100% guaranteed that while people say they're a master at CSS, there are probably only a miniscule amount of people who have read how CSS raste

It's also nearly 100% guaranteed that while people say they're a master at CSS, there are probably only a miniscule amount of people who have read how CSS rasterizers actually work. I'd almost bet there are probably more people who have reimplemented OpenGL in software than people who have read and understand how CSS compositors work. For example, if you asked someone how user agents create backing tiles for CSS, they'd look at you like you spoke in a foreign language. You totally don't need to know this stuff, but if you were doing say, high-perf UIs in WebKit (iOS), you'd probably at least want to know how to hint to WebKit that something needs its own render target or how to minimize subtree redraw. I built massively performant large UIs for payroll systems on iPad years ago and found that if you optimized your UI just right, you could get smooth scroll performance that showed cracks in how fast the iPad was able to draw backing tiles at the time. You'd get whole squares black scrolled into view while WebKit asynchronously drew in elements.