function changeBg(div) {
    var nav = document.getElementById(div);
    nav.style.background = "url('images/bgmain.gif')";
    nav.style.color = "white";
}
function returnBg(div) {
    var nav = document.getElementById(div);
    nav.style.background = "url('images/dian.gif')";
    nav.style.color = "#4e4e4e";
}