When i try add stylesheet with name main.css to Scene, I got following warning:

 WARNING: com.sun.javafx.css.StyleManager loadStylesheetUnPrivileged Resource "main.css" not found.

and style not applied.

When renamed main.css to style.css, works fine.

A bit of source code:

public class MainClass extends Application {

    public static void main(String[] args) {
        Application.launch(MainClass.class, args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        BorderPane borderPane = new BorderPane();

        Scene scene = new Scene(borderPane);
        stage.setScene(scene);
        stage.show();
        scene.getStylesheets().add("main.css");
    }
}

If "main" is reserved word, you need made specify it in a javadoc