Size of CSS almost doubled after 21.0.9

[ArthurClemens]

Size of CSS almost doubled after 21.0.9

[jonrohan]

Thanks for letting us know, this is alarming, going to see if there's some improvements we can make.

[keithamus]

This is due to supporting the ::backdrop selector, which does not inherit from :root in older browsers, requiring us to duplicate all of our variables into that selector. All the latest browsers now do inherit ::backdrop from :root but we still need to support older browsers, and so we'll need to continue this duplication for the next few years. They also need to be separate selectors because some very old browsers will throw away the whole selector if they don't recognise ::backdrop and so those very old browsers will lose all colour information.

While this increases size on disk, the gzip size (as in the over-the-wire size) isn't significantly impacted as it is duplicate data. I don't have the figures to hand but the total size increase is likely less than 1kb when gzipped. CSS is also very quick to parse so it's unlikely to add more than, say, 1ms to browser parse times.

Given the above reasons, I think we'll close this issue now as there's nothing directly actionable we can do. However in a few years when ::backdrop inheriting is better supported we can drop the duplicate data.