var message_box;
window.addEvent('domready', function() {

  message_box = document.getElement('.message_box');
  if (message_box) {
    setTimeout('hide_message_box()', 10000);
  }
});

function hide_message_box()
{
  var myEffects = new Fx.Morph(message_box, {duration: 1000});

  myEffects.start({
      'height': 0,
      'opacity' : 0,
      'padding' :0,
      'border' :0
  });

}