Haha, nice one!
If we're talking about things already in (reasonably mature) specs, it would be one of these:
- conic-gradient()
- attr() everywhere
- :focus-within
- backdrop-filter
- CSS rule nesting
But hey, it's a magic wand, so maybe things don't have to be in specs yet or even be implementable! In that case, it would be one of the following:
- :has() everywhere, not just in JS
- var() to refer to ANY property, not just custom properties
- element queries and generally style queries
- Making custom properties animatable right in CSS, no JS required