Styling of controls does'nt work programmatically

Question

Hallo,
     I have a stylesheet (mystylesheet.css) with following entry:
.flowpane{
    -fx-background-color: rgb(0,0,0);
in then start-method of my application I execute:
        StackPane root = new FlowPane();
        Scene scene = new Scene(root,primaryScreenBounds.getWidth(),primaryScreenBounds.getHeight());
        scene.getStylesheets().add(css.getFile());
        root.applyCss();
no FlowPane gets black. But if I do that in SceneBuilder and add the stylesheet to root than after loading Fxml-file the FlowPane gets black.
Another approach:
        StackPane root = new FlowPane();
        Scene scene = new Scene(root,primaryScreenBounds.getWidth(),primaryScreenBounds.getHeight());
        scene.getStylesheets().add(css.getFile());
        root.getStyleSheets().add(css.getFile());
        root.applyCss();
Nothing happens.
        StackPane root = new FlowPane();
        Scene scene = new Scene(root,primaryScreenBounds.getWidth(),primaryScreenBounds.getHeight());
        scene.getStylesheets().add(css.getFile());
        root.getStyleSheets().add(css.getFile());
        root.getStyleClass().add("flowpanel"); 
        root.applyCss();
Does'nt work too;
but root.setStyle("-fx-background-color: rgb(0,0,0) works. But I need to style my application by css-files.
What I'm doing wrong?
with regards
Rafal Ziolkowski

Answer 1

The way I usually add stylesheets to a scene for simple programs that aren't using FXML is to invoke the following line from the application:
scene.getStylesheets().add(MyApplication.class.getResource("mystyles.css").toExternalForm());
Where mystyles.css is placed in the same directory as your Java source file and the project build process copies it to your project output directory (e.g. it will be copied to the same location as the application class file).  Optionally the build process can package the app up into something like an executable jar file.  So if you build is doing that you can unjar the jar file and check that your css is in there in the correct location next to your main application class.
I have no idea what css.getFile() is in your code, so it is impossible to comment on what that may do.  It is usually best for questions like this to provide a complete minimal executable that somebody could just copy and paste to run.  Also if there is any stack trace generated, then you should include the complete stack trace in your question.