There is my first question and I welcome community!
I'm making a simple game and have some problems with Start menu.

I have three buttons on my JPanel StartMenu and when I click "Settings" button, new JPanel will be open, but I don't know why buttons from StartMenu JPanel appeared in my Settings JPanel.

My "Settings" JPanel has one ugly button "Back" in center and ugly grey background.

I made some screens to see a problem.

Start Menu JPanel when game launched

Settings JPanel when button clicked

Settings JPanel when mouse was over settings window

There is code of StartMenu class:

public class StartMenu extends JPanel {
    private GameButton startGameButton = new GameButton("Start game");
    private GameButton settingsGameButton = new GameButton("Settings");
    private GameButton exitGameButton = new GameButton("Exit game");
    private Image bgImage = new ImageIcon(getClass().getClassLoader().getResource("ru/andydevs/astraLaserForce/bg.png")).getImage();
    private int posX;
    private int posY;
    final private int WIDTH=(int)Game.SCREEN_DIMENSION.getWidth()/3;
    final private int HEIGHT=(int)Game.SCREEN_DIMENSION.getHeight()/2;

    public StartMenu() {
        setLayout(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();
        setSize(new Dimension(WIDTH, HEIGHT));

        posX=(int)Game.SCREEN_DIMENSION.getWidth()/2-WIDTH/2;
        posY=(int)Game.SCREEN_DIMENSION.getHeight()/2-HEIGHT/2;
        setBounds(posX, posY,WIDTH,HEIGHT);

        c.ipadx=95;
        c.ipady=15;

        c.fill = GridBagConstraints.HORIZONTAL;
        c.insets = new Insets(20,0,0,0);
        c.gridy=0;
        add(startGameButton, c);

        c.gridy=1;
        c.insets = new Insets(20,0,0,0);
        System.out.println(settingsGameButton.getWidth());
        add(settingsGameButton, c);

        c.gridy=2;
        c.insets = new Insets(20,0,0,0);
        add(exitGameButton, c);

        settingsGameButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                GameOptionsPanel gop = new GameOptionsPanel();
                Game.container.add(gop);
                Game.container.setComponentZOrder(gop, 0);
                Game.container.revalidate();
                Game.container.repaint();

            }
        });

        exitGameButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                Main.currentGame.stop();
            }
        });
    }

    public void paintComponent(Graphics g) {
        g.drawImage(bgImage,0,0,WIDTH,HEIGHT,null);
    }

}

There is code of Settings JPanel

public class GameOptionsPanel extends GamePanel {
    private GameButton backButton = new GameButton("Back");
    private GameOptionsPanel that;
    public GameOptionsPanel() {
        super((int) (Game.SCREEN_DIMENSION.getWidth()/3), (int) (Game.SCREEN_DIMENSION.getHeight()/2), new Color(50,50,50));
        that=this;

        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();

        gbc.fill=gbc.HORIZONTAL;

        add(backButton);

        backButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                Game.container.remove(that);
                Game.container.revalidate();
                Game.container.repaint();
            }
        });

    }
}

I glad to see some suggestions. Thanks.