In http://javafx-jira.kenai.com/browse/RT-19713 we are adding API to allow setting of the user agent stylesheet from code. If we are going to change the default value for user agent stylesheet in 8 we want to make it as easy as possible for existing applications to switch back to caspian.css if they need to for compatibility reasons. So adding a system property that would allow this switch from the command line makes a lot of sense. Proposed by Daniel Zwolenski on openjfx dev mailing list.