How to make background of modal popup darker and non transparent in unity? - unity3d

Question

I have a modal pop up in which I show a list of stories title and a button to open a browser that points the link of the stories, but the pop up is now transparent I want the background to appear darker
Need to modify my modal pop up without a transparent background or make the background color darker, or how can I change the GUI modals opaque or can I set opaque value for this GUI?
please check my modal pop up code here:
using UnityEngine;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
// example:
// HFTDialog.MessageBox("error", "Sorry but you're S.O.L", () => { Application.Quit() });
public class HFTDialog : MonoBehaviour {
Rect m_windowRect;
Action m_action;
string m_title;
string m_msg;
string[] m_myNewsTitleColl;
string[] m_myColl;
GUIStyle labelStyle, labelStyleShadow, buttonStyle, sliderStyle, sliderThumbStyle;
// The position on of the scrolling viewport
public Vector2 scrollPosition = Vector2.zero;
private GUIStyle guiStyle; //create a new variable
static public void MessageBox(string[] myNewsTitleColl, string[] myColl,string title, string msg, Action action)
{
GameObject go = new GameObject("HFTDialog");
HFTDialog dlg = go.AddComponent<HFTDialog>();
dlg.Init(myNewsTitleColl,myColl,title, msg, action);
}
static public void CloseMessageBox(GameObject go)
{
Destroy(go.gameObject);
}
void Init( string[] myNewsTitleColl,string[] myColl,string title, string msg, Action action)
{
m_title = title;
m_msg = msg;
m_action = action;
m_myColl=myColl;
m_myNewsTitleColl=myNewsTitleColl;
}
void OnGUI()
{
const int maxWidth = 640;
const int maxHeight = 480;//480;
int width = Mathf.Min(maxWidth, Screen.width - 20);
int height = Mathf.Min(maxHeight, Screen.height - 20);
m_windowRect = new Rect(
(Screen.width - width) / 2,
(Screen.height - height) / 2,
width,
height);
GUI.color = Color.white;
GUI.backgroundColor = Color.yellow;
m_windowRect = GUI.Window(0, m_windowRect, WindowFunc, m_title);
}
void WindowFunc(int windowID)
{
const int border = 10;
const int width = 50;
const int height = 25;
const int spacing = 10;
guiStyle = new GUIStyle();
//guiStyle.fontSize = 14; //change the font size
guiStyle.fontStyle = FontStyle.Bold;
guiStyle.normal.textColor = Color.white;
int myNewsTitlePositionY=border + spacing;//Initial position
if(m_myNewsTitleColl.Length==0){
Rect l = new Rect(border, myNewsTitlePositionY,m_windowRect.width - border * 2,m_windowRect.height - border * 2 - height - spacing);
GUI.Label(l, "Currently No News Available ,Please try later..",guiStyle);//This is the news title label
}
else{
for(var i = 0; i < m_myNewsTitleColl.Length; i++)
{
var NewsTitle = m_myNewsTitleColl[i];
Rect l = new Rect(border, myNewsTitlePositionY,m_windowRect.width - border * 2,m_windowRect.height - border * 2 - height - spacing);
GUI.Label(l, NewsTitle,guiStyle);//This is the news title label
myNewsTitlePositionY=myNewsTitlePositionY+33;//next y position of the news title label
}
}
int myY=-15;
for(var i = 0; i < m_myColl.Length; i++)
{
var item = m_myColl[i];
// work with link item here to make a button
myY=myY+33; //Y position of button
Rect btn = new Rect(550,myY, width+25, height);
//Rect btn = new Rect(510,myY, width+25, height); //when scroll enable -
if (GUI.Button(btn, "Open Link"))
{
//open browser pointing the url
Application.OpenURL(item);
}
Debug.Log ("from string array value is :"+item);
}
//End Scrollview
// GUI.EndScrollView();
Rect b = new Rect(
m_windowRect.width - width - border,
m_windowRect.height - height - border,
width,
height);
if (GUI.Button(b, "close"))
{
Destroy(this.gameObject);
// m_action();
}
}
}