My code disappear

[pan]

HTML part disappear

HTML

PHP Code:

<a href="#" class="greenhead"
onclick="style.background='url(http://i.cubeupload.com/Gi4rVR.png) ' "></a> 


CSS

PHP Code:

.greenhead {
  width: 200px;
  height: 200px;
  display: block;
  border: 0px;
  background: url('http://i.cubeupload.com/TYeudm.png');
}

.greenhead:hover {
  background: url('http://i.cubeupload.com/lYu4hD.png');
}