function setDown(x) {
  var obj = document.getElementById(x);
  obj.className += "_down";
}

function startHover(x) {
  var obj = document.getElementById(x);
  obj.oClassName = obj.className;
  obj.className += "_hover";
}

function endHover(x) {
  var obj = document.getElementById(x);
  obj.className = obj.oClassName;
}