StyleX compiled nothing in .astro files. The cause was one missing extension in a filter, and the reason nobody noticed was an example that avoided the broken path.
Neither half failed loudly. The build threw at render, and once that was fixed the page still shipped with no stylesheet linked at all.
Atomic CSS cannot rely on source order, so StyleX repeats:not(#\#) to rank properties by how specific they are. Shorthands sit at the bottom, longhands above them. Each rung here is one more repetition.
The fix is one line in @stylexjs/unplugin, applied here through pnpm patch so this repo runs without a local checkout of StyleX. Seethe index for what compiles.
This paragraph is styled through attrs() and carries a viewTransitionClass.