function darken(vis,arg) {

  var dark=document.getElementById('darklayer');

  if (vis) {
     if (document.body && (document.body.scrollWidth || document.body.scrollHeight)) {
        var pageWidth = document.body.scrollWidth+'px';
        var pageHeight = document.body.scrollHeight+'px';
     } else if (document.body.offsetWidth) {
        var pageWidth = document.body.offsetWidth+'px';
        var pageHeight = document.body.offsetHeight+'px';
     } else {
        var pageWidth='100%';
        var pageHeight='100%';
     }

     if (arg =='msg') {
        var pageWidth='100%';
        var pageHeight='100%';
     }

     dark.style.width=pageWidth;
     dark.style.height=pageHeight;
     dark.style.display='block';
  } else {
     dark.style.display='none';
  }
}

function hidemsg() {
  var abox=document.getElementById('alertbox');
  var dark=document.getElementById('darklayer');
  abox.style.visibility='hidden';
  dark.style.display='none';
}