//display or hide the part of the menu that the user clicks
function ShowHideMenu(menuID){

   //change the menu div that was clicked by the user to its opposite state
   var menuID = document.getElementById(menuID);

        if (menuID.style.display != "none") {

            //items are currently displayed, so hide them
            menuID.style.display = "none";

        }
        else {

            //items are currently hidden, so display them
            menuID.style.display = "block";

        }

    }