Not able to apply Styling in ControlFX Popover

Question

In my project I am using controlfx popover, I have tried a lot to put style class, below are code snippet but am failing to do so

popOver.getSkin().getNode().setStyle("-fx-border-color: GREEN");

((Parent) popOver.getSkin().getNode()).setStyle("-fx-border-color: GREEN;-fx border-width: 5px;-fx-background-color:GREEN")

Thanks,any help would be appreciated.