chromium/content/test/data/page_with_animation.html

<!doctype html>
<html>
  <head>
    <style>
      @keyframes move {
        from {
          transform: translate(-200px, 0);
        }
        to {
          transform: translate(200px, 0);
        }
      }

      div {
        height: 200px;
        width: 200px;

        animation-duration: 1.5s;
        animation-iteration-count: infinite;
        animation-name: move;

        background: black;
      }
    </style>
  </head>
  <body>
    <div></div>
  </body>
</html>