Concrete issue: It is not possible to create CSS styling for a Button with an ImageView where the disabled state is not defined by -fx-opacity but with a certain color definition.

See https://community.oracle.com/message/11334752

If I do this, the icon is not greyed. To be able to define custom css stylings it is necessary that all kinds of Nodes (and in my case the ImageView) get a default style class. Otherwise it is not possible to define styles with full flexibility by just using CSS.