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

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

document.onmouseover = rollon;
document.onmouseout = rolloff;