JIT: Optimize universal selector usage by inlining only the relevant selectors #4850
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Currently (especially in JIT) we make heavy use of the universal selector (
*
) to do these sort of "resets" for composable utilities,transform
for example:It turns out reading/writing to CSS variables can be expensive on site that have a lot of DOM nodes (like the Tailwind CSS home page) and that causes things to render more slowly than they really should have to if you only apply those rules when needed.
This PR adds a separate optimization step that ensures what used to be the universal selector is replaced with only the selectors needed, so the output looks more like:
...where the selectors included are all of the ones used in your template files that depend on this reset.
To make this work, we've added a new
@defaults
at-rule, which we consider private API for now until we're sure it's the correct abstraction.