body, html {
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 0;

  text-align: center;
}

#container {
  width: 640px;
  height: 480px;
  margin: 20px auto;
}

#container.fullscreen {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}