animations.css

/*
  Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
  for details. All rights reserved. Use of this source code is governed by a
  BSD-style license that can be found in the COPYING file.
*/

.mover {
  position: absolute;
  width: 100px;
  height: 100px;
  background: url(http://1-ps.googleusercontent.com/x/s.html5rocks-hrd.appspot.com/www.html5rocks.com/en/tutorials/speed/animations/particle.png.pagespeed.ce.jWkhaHzlBa.png) center no-repeat;
  left: 90%;
  -webkit-transition: left 1.3s ease-out;
  -moz-transition: left 1.3s ease-out;
  -ms-transition: left 1.3s ease-out;
  -o-transition: left 1.3s ease-out;
  transition: left 1.3s ease-out;
}

.mover.left {
  left: 10%;
}