function rollon() {
  if (window.event.srcElement.className == "item") {
    window.event.srcElement.className = "highlight"; // change class
  }
}

function rolloff() {
  if (window.event.srcElement.className == "highlight") {
    window.event.srcElement.className = "item"; // change class
  }
}

// assign rollon() to handle onMouseOver events
document.onmouseover = rollon;

// assign rolloff() to handle onMouseOut events
document.onmouseout = rolloff;