One thing with native CSS nesting that is constantly catching me off-guard is that you can't nest inside of pseudo-classes/elements. Was playing with popovers and you can't put a @​starting-style inside of :popover-open... took me way to long to realize what was wrong. I knew this was a limitation of how it works with pseudo-elements, so I should have realized it sooner... so I'm partially writing this to let others know, and also hoping it helps me remember 😆