GUI Texture Pause Button

 #pragma strict
 
  var totalScore : int = 0;
  var temp : int = 0;
  var higestDistance = 0;
  var scoreInfoVariable : GUIText;
  
  var fpc :GameObject;
  internal var showMenu : boolean = false;
  
  var platform06 : GameObject;
  
  function Start () {
      Screen.showCursor = false;
  }
  
  function Update () {
      if (Input.GetKeyDown ("escape")){
          if (Screen.showCursor == false) {
              fpc.SendMessage("ToggleInputCursor", true);
              Screen.showCursor = true;
              showMenu = true;
              Time.timeScale = 0;
          }
          else {
              ResumeGame();
          }
      }
  }
  
  function UpdateScoreInfoGUI( distance : int) {
      totalScore = totalScore + distance;
      scoreInfoVariable.text = ""+ totalScore;
  }
  
  function ActivatePlatformPrefab06(){
      platform06.active = true;
      print("message is received");
  }
  
  function OnGUI(){
      if(showMenu == true)
      {
          GUI.BeginGroup(Rect(Screen.width/2 - 50, Screen.height/2 - 50, 100, 90));
          
          GUI.Box(Rect(0, 0, 100, 90), "Menu");
          if(GUI.Button(Rect(10, 30, 80, 20), "Resume")){
              print("you clicked  RESUME");
              ResumeGame();
          }
          if(GUI.Button(Rect(10, 60, 80, 20), "Quit")){
              print("you clicked  QUIT");
              Application.Quit();
          }
          
          GUI.EndGroup();
      }
  } 
  
  function ResumeGame(){
              Screen.showCursor = false;
              fpc.SendMessage("ToggleInputCursor", false);
              showMenu = false;
              Time.timeScale = 1.0;
  }

Hi Guys; This my code and i don't know how can i add GUI Skin in code.

When i click this button show menu.How can i do this.

NOTE: It's android game so how can i replace Input.GetKeyDown to GUI skin button.

Thanks For reading.