function rollon() {
  if (window.event.srcElement.className == "leftnavdown") {
    window.event.srcElement.className = "leftnavup";
  }
}

function rolloff() {
  if (window.event.srcElement.className == "leftnavup") {
    window.event.srcElement.className = "leftnavdown";
  }
}

document.onmouseover = rollon;

document.onmouseout = rolloff;