I wonder if it allows for no js fallback? @matuzo.at you may be able to put something static between the tags and then use baseline-status:define to hide it?
This friend here 👇 is HTML / CSS and my site is 11ty, too. I never bothered to make it a proper module (or plugin) but I'm happy to share the source code if you want to implement it or polish it for someone else to use.
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I have this code running for a couple of years now. The only thing that happens occasionally is that MDN compat data changes and it break my build.
But it really only happened a couple of times, so i think it's fine.
https://gist.github.com/stefanjudis/3b13a642ec9570e2b7983385199b3114