function showtab1 () {
  if (document.getElementById)
    document.getElementById("tab1").style.display = "inline";
    document.getElementById("tab2").style.display = "none";
    document.getElementById("tab3").style.display = "none";
    document.getElementById("navi1").className = "tabon";
    document.getElementById("navi2").className = "taboff";
    document.getElementById("navi3").className = "taboff";

};

function showtab2 () {
  if (document.getElementById)
    document.getElementById("tab1").style.display = "none";
    document.getElementById("tab2").style.display = "inline";
    document.getElementById("tab3").style.display = "none";
    document.getElementById("navi1").className = "taboff";
    document.getElementById("navi2").className = "tabon";
    document.getElementById("navi3").className = "taboff";

};

function showtab3 () {
  if (document.getElementById)
    document.getElementById("tab1").style.display = "none";
    document.getElementById("tab2").style.display = "none";
    document.getElementById("tab3").style.display = "inline";
    document.getElementById("navi1").className = "taboff";
    document.getElementById("navi2").className = "taboff";
    document.getElementById("navi3").className = "tabon";

};