// ändert das Sichtbare untermenü
function chsubmenu (id) {
  invisible_sub();
  document.getElementById(id).style.visibility = "visible";
}

// ändert das unterunter-Menü (bei Produkte)
function chsubsub(id) {
  invisible_subsub();
  document.getElementById(id).style.visibility = "visible";
}

// alle Submenüeinträge ausblenden
function invisible_sub () {
 invisible_subsub();
 document.getElementById('sub_home').style.visibility = "hidden";
 document.getElementById('sub_ueberuns').style.visibility = "hidden";
 document.getElementById('sub_produkte').style.visibility = "hidden";
 document.getElementById('sub_partner').style.visibility = "hidden";
 document.getElementById('sub_support').style.visibility = "hidden";
 document.getElementById('sub_kontakt').style.visibility = "hidden";
}

// alle Unteruntermenüeinträge ausblenden
function invisible_subsub() {
 document.getElementById('alleprodukte').style.visibility = "hidden";
}