function PopupCentrata() {
   var w = 600;
   var h = 600;
   var l = Math.floor((screen.width-w)/2);
   var t = Math.floor((screen.height-h)/2);
   var stile = ", status=nu, menubar=nu, toolbar=no, scrollbars=no";
      window.open("offerte.htm","","width=" + w + ",height=" + h + ",top=" + t + ",left=" + l + stile );
 }