<!DOCTYPE html>
<html class="reftest-wait">
  <head>
  </head>
  <body>
    <div id="host"></div>
    <script>
      var host = document.getElementById("host");
      var root = host.createShadowRoot();
      root.innerHTML = '<style>input ~ div { background: red; transition: background 100ms; } input:checked ~ div { background: green; }</style><input id="one" type="checkbox"><div style="height: 50px; width: 50px;"></div>';

      function tweak() {
          var el = root.getElementById("one");
          el.checked = true;
          el.nextSibling.addEventListener("transitionend", function() {
            document.documentElement.removeAttribute("class");
          }, false);
      }

      window.addEventListener("MozReftestInvalidate", tweak, false);
    </script>
  </body>
</html>