style sheet assignments are done on Scene level.This is not necessarily true.
Beginning with JavaFX 2.1, the Parent class has a stylesheets property, allowing style sheets to be set on a container. This allows for one branch of of the scene graph to have a distinct set of styles. Any instance of Parent can have a style sheets. A child will take its styles from its own inline styles, the style sheets of all its ancestors, and any style sheets from the Scene.