function tabbox(what) {
  if(what == "News") {
    document.getElementById("News").style.visibility = "visible";
    document.getElementById("Veranstaltungen").style.visibility = "hidden";
    document.getElementById("Workshops").style.visibility = "hidden";
    document.getElementById("Webinare").style.visibility = "hidden";
    document.getElementById("liNews").className = "active";
    document.getElementById("liVeranstaltungen").className = "";
    document.getElementById("liWorkshops").className = "";
    document.getElementById("liWebinare").className = "";
  }
  if(what == "Veranstaltungen") {
    document.getElementById("News").style.visibility = "hidden";
    document.getElementById("Veranstaltungen").style.visibility = "visible";
    document.getElementById("Workshops").style.visibility = "hidden";
    document.getElementById("Webinare").style.visibility = "hidden";
    document.getElementById("liNews").className = "";
    document.getElementById("liVeranstaltungen").className = "active";
    document.getElementById("liWorkshops").className = "";
    document.getElementById("liWebinare").className = "";
  }
  if(what == "Workshops") {
    document.getElementById("News").style.visibility = "hidden";
    document.getElementById("Veranstaltungen").style.visibility = "hidden";
    document.getElementById("Workshops").style.visibility = "visible";
    document.getElementById("Webinare").style.visibility = "hidden";
    document.getElementById("liNews").className = "";
    document.getElementById("liVeranstaltungen").className = "";
    document.getElementById("liWorkshops").className = "active";
    document.getElementById("liWebinare").className = "";
  }
  if(what == "Webinare") {
    document.getElementById("News").style.visibility = "hidden";
    document.getElementById("Veranstaltungen").style.visibility = "hidden";
    document.getElementById("Workshops").style.visibility = "hidden";
    document.getElementById("Webinare").style.visibility = "visible";
    document.getElementById("liNews").className = "";
    document.getElementById("liVeranstaltungen").className = "";
    document.getElementById("liWorkshops").className = "";
    document.getElementById("liWebinare").className = "active";
  }
}