How do you make a script to close out this pop up menu?

Title explains it all, I suck at coding some things. I've been trying to do stuff for a while, and still can't get it.

Here is code:

 using UnityEngine;
 using System.Collections;
 
 public class Popup : MonoBehaviour {
     public Rect windowRect = new Rect(200, 200, 1200, 500);
     void OnGUI() {
         windowRect = GUI.Window(0, windowRect, DoMyWindow, "Controls: WASD/Arrow Keys: Move | R: Reset| Esc: Quit Game" +
             " || New Features: This Popup Of Course.| Day And Night System.|| Running Version 3");
     }
     void DoMyWindow(int windowID) {
         if (GUI.Button (new Rect (10, 20, 100, 20), "Ok, Whatever"))
             show windowRect = false;
         
     }
 }