CSS splitting on production builds

[intrnl]

Is your feature request related to a problem? Please describe.
Large apps might have large CSS bundles, and most of the time not all of it is useful when you only look at a single page.

Describe the solution you'd like
Those kinds of apps usually have lazy loaded components and routes already, and those are automatically split into individual chunks, so it would be great if the CSS is also split into individual chunks too.

Describe alternatives you've considered
Using CSS-in-JS, putting individual styles on the public folder and then importing them later on. The latter isn't doable of course, and the former doesn't really fit everyone's taste buds.

Additional context
None.

[yyx990803]

Yeah, this is something on the roadmap.