For a stylesheet added using Parent.getStylesheets().add(...), I found that properties defined in a ".root" element were not accessible in other elements of the same stylesheet. In contrast, properties defined in the root element of the scene stylesheet were accessible by the elements in the parent stylesheet. While I can see this could be very useful, it is not what I need for my application. Having a root for the parent stylesheet would be much more useful for me.

For this use case, I only care about using the root from the parent so I don't have a strong opinion on the relationship between the scene root and the parent root. Probably, the most useful solution would be if properties in the parent root can override properties in the scene root.