Support inlining critical CSS for faster core web vitals

Adding API support is a good idea, we could try to implement it in Olivero too maybe.

✨ Allow CSS to be added at end of page by rendering assets with placeholders Active is trying to defer CSS.

Are you adding this to individual files or the library definition? And what happens if a critical file has a dependency on a non-critical one?

✨ [PP-2] Support inline and async CSS Postponed: needs info is already open but there was no progress there and I marked it 'needs more info' some time ago, so possibly we should start fresh and mark that issue duplicate of this.

Pushed up some work based on our client projects but it doesn't work with asset aggregation turned on - that's because the file doesn't exist the first time around.

It works on our client project because we have build tooling for CSS so don't use core's aggregation for the FE theme

Will have to have a think about how to do this in a way that is compatible with the lazy asset optimization/rendering.

Added preprocess: false to the inline items for now, but ideally we could automate that. Perhaps we need to move critical up to the top level of the definition

Added a test

Maybe something like this?

global:
  css:
    critical:
       css/critical-stuff.css: {}
    base:
       css/normal-stuff.css: {}

Reads a bit better, but probably changes the whole implementation :)

This feature would allow the Inline All CSS → module to continue to live in Drupal 11+.