Java GUI - 按钮不会添加到面板

Question

您好我在向GUI添加按钮时遇到问题，我尝试使用BorderLayout添加按钮但是在运行时它没有显示。由于使用BorderLayout，我选择的背景颜色也会恢复为白色。有人可以帮忙吗？

import javax.swing.*;
import java.awt.*;

public class BlackjackGUI{

    private JFrame frame;
    private JPanel panel;
    private JButton newGameBtn, dealBtn, hitBtn, standBtn;
    private JLabel playerMoneyLbl;
    private JLabel playerCard1Lbl, playerCard2Lbl, playerCard3Lbl,
                   playerCard4Lbl, playerCard5Lbl, playerCard6Lbl, playerCard7Lbl;
    private JLabel dealerCard1Lbl, dealerCard2Lbl, dealerCard3Lbl, dealerCard4Lbl,
                   dealerCard5Lbl, dealerCard6Lbl, dealerCard7Lbl;  
    private JLabel playerCardValueLbl, dealerCardValueLbl;
    private JTextField betInputBox;

    public BlackjackGUI(){
        createForm();
        addButtons();

        frame.add(panel);
        frame.setVisible(true);
    }

    public void createForm() {
        JFrame frame = new JFrame("Blackjack");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(1200,800);
        frame.setVisible(true);

        JPanel panel = new JPanel();
        Color c = new Color(0, 100, 0);
        panel.setBackground(c);
        panel.setLayout(new BorderLayout());

    }

    public void addButtons() {

        newGameBtn = new JButton("New Game");
        panel.add(newGameBtn, BorderLayout.NORTH);

    }

    public static void main(String[] args) {
    new BlackjackGUI();

    }

}