Context menu has extra area when I set CSS ( .root{ -fx-background-color or -fx-background-image }) to scene on Java8.
on Java7 : http://i.imgur.com/xm3SRoj.jpg
on Java8 : http://i.imgur.com/xtU7HQj.jpg

・code

@Override
public void start(Stage primaryStage) {
    MenuBar bar = new MenuBar();
    Menu menu = new Menu("File");
    MenuItem item = new MenuItem("exit");
    menu.getItems().add(item);
    bar.getMenus().add(menu);
    bar.setPrefWidth(300);
    
    AnchorPane root = new AnchorPane();
    root.setStyle("-fx-background-color: white;");
    root.getChildren().add(bar);
    AnchorPane.setTopAnchor(bar, 0.0);
           
    Scene scene = new Scene(root, 300, 250);
    scene.getStylesheets().add(this.getClass().getResource("/javafxapplication/style.css").toExternalForm());
    
    primaryStage.setTitle("Hello World!");
    primaryStage.setScene(scene);
    primaryStage.show();
}


・style.css

.root{
    -fx-background-color: red;
}