public class Main extends Application {


    private Boolean buttonPressed = false;


    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {

        BorderPane appWindow = new BorderPane();
        appWindow.setStyle("-fx-alignment: center; -fx-padding: 30 0 0 30");
        appWindow.setBackground(new Background(new BackgroundFill(Color.PERU, null, null)));
        GridPane loginContainer = new GridPane();
        appWindow.setCenter(loginContainer);

        TextField username = new TextField();
        PasswordField password = new PasswordField();
        Label userNameDesc = new Label("Username");
        Label passwordDesc = new Label("Password");
        Button logInBtn = new Button("Log In");

        logInBtn.setTranslateX(100);
        logInBtn.setTranslateY(20);

        logInBtn.setOnAction(event -> {

            if (!buttonPressed) {
                appWindow.getCenter().setOpacity(30);
                buttonPressed = true;
                System.out.println("Opacity set to " + appWindow.getCenter().getOpacity());
            }

            else {
                appWindow.getCenter().setOpacity(100);
                buttonPressed = false;
                System.out.println("Opacity set to " + appWindow.getCenter().getOpacity());
            }

        });

        loginContainer.addColumn(0, userNameDesc, passwordDesc);
        loginContainer.addColumn(1, username, password);
        loginContainer.add(logInBtn, 1, 2);

        Scene scene = new Scene(appWindow, 300, 250);
        stage.setScene(scene);
        stage.show();
    }
}