Added the back Button to the GUI

src/main/java/game/StartTicTacToeGame.java

@@ -98,6 +98,15 @@ public class StartTicTacToeGame implements ActionListener{
 		button9.setBounds(500, 400, 100,100);
 		button9.addActionListener(this);
 		gui.Frame.add(button9);
+		
+		backButton = new JButton();
+		backButton.setBackground(Color.white);
+		backButton.setBounds(350,400, 100,50);
+		backButton.addActionListener(this);
+		backButton.setVisible(false);
+		backButton.setFont(new Font("arial", Font.PLAIN, 16));
+		backButton.setText("Zurück");
+		gui.Frame.add(backButton);
 	}