/* Background */
color {
  bounds: 0 0 200 200;
  color: white;
}

/* It is important that the following node structure leaves the
 * start child of the cross-fade node invisible. */
opacity {
  opacity: 0.4;

  child: cross-fade {
    start: color {
      color: blue;
      bounds: 0 0 100 100;
    }
    end: color {
      color: red;
      bounds: 100 100 100 100;
    }
    progress: 1.0;
  }
}