add close button to script

how would i add a close button to this script to make the gui close thanks

 var information: String; 
 private var guiOn = false;
 private var rect: Rect;
 var btnTexture : Texture;
 
 function OnMouseDown(){
     guiOn = true; 
     rect = Rect(Input.mousePosition.x, Input.mousePosition.y, 300, 100);
     yield WaitForSeconds(500);
     guiOn = false;
 }
 
 function OnGUI(){
     if (guiOn){
         GUI.Box(Rect(0,0,200,200),"Current bid");
         if (!btnTexture) {
             Debug.LogError("Assign a texture");
             return;
         }
         if (GUI.Button(Rect(10,10,50,50),btnTexture))
             Debug.Log("Image Button");
         if (GUI.Button(Rect(10,70,50,30),"Bid"))
             Debug.Log("Text button");
             
     
     }
 }