function vertical() { 

   var navItems = document.getElementById("nav").getElementsByTagName("li"); 
    
   for (var i=0; i< navItems.length; i++) { 
      if(navItems[i].className == "submenu") { 
         navItems[i].onmouseover=function() {this.getElementsByTagName('ul')[0].style.display="block";} 
         navItems[i].onmouseout=function() {this.getElementsByTagName('ul')[0].style.display="none";} 
      } 
   } 

}