Changing Font/color on a GUI

I'm trying to change the font/color on a GUI using GUISkin (or GUIStyle, whichever will work). Here is my code it's attached to a menu.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class Menu : MonoBehaviour
{
public int MenuWidth;
public int MenuHeight;
public Texture Image;
public GUIStyle GUIStyle; // set the text style of the frame counter
Rect MenuRect;


// Start is called before the first frame update
void Start()
{


if ((MenuWidth == 0) || (MenuHeight == 0))
{
Debug.Log("Menu size isn't set");
}
MenuRect = new Rect(Screen.width / 2 - MenuWidth / 2, Screen.height / 2 - MenuHeight / 2, MenuWidth, MenuHeight);

}


// Update is called once per frame
void Update()
{

}


private void OnGUI()
{
GUI.Box(MenuRect, "Main Menu");

GUI.DrawTexture(new Rect(Screen.width / 2 - 30, MenuRect.yMin + 30, 50, 50), Image);

if (GUI.Button(new Rect(MenuRect.xMin + 20, MenuRect.yMin + 130, MenuRect.width - 100, 100), "PLAY"))
{
SceneManager.LoadScene(1);
}

if (GUI.Button(new Rect(MenuRect.xMin + 20, MenuRect.yMin + 225, MenuRect.width - 50, 100), "QUIT"))
{
Application.Quit();
}
}

I keep getting console errors, or the information shows up in the inspector but changing the inspector values doesn't change anything in the GUI.

 

This is my other more error filled attempt

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class Menu : MonoBehaviour
{
public int MenuWidth;
public int MenuHeight;
public Texture Image;
public GUIStyle GUIStyle; // set the text style of the frame counter
Rect MenuRect;
// Create a public variable where we can assign the GUISkin
var customSkin : GUISkin;


// Start is called before the first frame update
void Start()
{


if ((MenuWidth == 0) || (MenuHeight == 0))
{
Debug.Log("Menu size isn't set");
}
MenuRect = new Rect(Screen.width / 2 - MenuWidth / 2, Screen.height / 2 - MenuHeight / 2, MenuWidth, MenuHeight);

}


// Update is called once per frame
void Update()
{

}


private void OnGUI()
{
GUI.skin = customSkin;

GUI.Box(MenuRect, "Main Menu");

GUI.DrawTexture(new Rect(Screen.width / 2 - 30, MenuRect.yMin + 30, 50, 50), Image);

if (GUI.Button(new Rect(MenuRect.xMin + 20, MenuRect.yMin + 130, MenuRect.width - 100, 100), "PLAY"))
{
SceneManager.LoadScene(1);
}

if (GUI.Button(new Rect(MenuRect.xMin + 20, MenuRect.yMin + 225, MenuRect.width - 50, 100), "QUIT"))
{
Application.Quit();
}
}

}