This idea comes from Jasper during a discussion we had at J1. SDK team has possible plans to add a styleSheets setter in the container hierarchy. This setter would GREATLY SIMPLIFIED the way we handle CSS in the Scene Builder.
2 major advantages:
1) The CSS files path that are set in the SceneBuilder will be stored in the FXML in a standard way. Today we have a special XML processing instruction to keep references.
2) The AUthor CSS rules will be easily scoped inside the root node of the user content. We have currently to rewrite the CSS rules with a prefix.

This RFE would cleanup a big part of our current support. Having it for 2.0.4 would be good for our public release.