function positiondropdown() {
  var browser = navigator.appName;
  var cw = 960;
  if (browser == "Microsoft Internet Explorer")
    cw = document.body.clientWidth;
  else if (browser == "Netscape")
    cw = window.innerWidth - 20;
    
  var left = 0;
  if (cw > 960) {
    left = Math.ceil((cw - 960) / 2);
  }
  
  var realleft = left + 846;
  document.getElementById("divDropdown").style.left = realleft + "px";
}

function showdropdown() {
  document.getElementById("divDropdown").style.display = "";
}

function hidedropdown() {
  document.getElementById("divDropdown").style.display = "none";
}