<!DOCTYPE HTML>
<html>
<head>
  <script>
    function tweak() {
      // div with style "border: 10px solid green"
      var shadowDiv = document.createElement("div");
      shadowDiv.style.border = "10px solid green";

      // Insertion point will match nothing and use fallback content.
      var insertionPoint = document.createElement("content");
      shadowDiv.appendChild(insertionPoint);

      // Append three nodes as children to use as fallback content.
      insertionPoint.innerHTML = '<span style="background-color: orange">Hello</span> <span style="background-color: green">World</span>';

      var shadowRoot = document.getElementById('outer').createShadowRoot();
      shadowRoot.appendChild(shadowDiv);
    }
  </script>
</head>
<body onload="tweak()">
<div id="outer"></div>
</body>
</html>