text: window.onscroll = function() {toTopDisplay();}
  
  function toTopDisplay(){            //to display toTopButton only when scrolled below the entrance screen
      if(document.documentElement.scrollTop > 150){
          document.getElementById("toTopButton").style.display = "block";
      }else{
          document.getElementById("toTopButton").style.display = "none";
      }
  }
  
  function scrollToTop(){         //scroll top top of web page
      document.documentElement.scrollTop = 0;
  }     
  