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<!-- Any copyright is dedicated to the Public Domain.
<html>
<head>
  <title>CSSOM test</title>
  <script>
    "use strict";
    window.onload = function() {
      const x = document.styleSheets[0];
      x.insertRule("div { color: seagreen; }", 1);
      // Add a rule with a leading newline, to test that inspector can handle it.
      x.insertRule("\ndiv { font-weight: bold; }", 1);
      // Add a shadow dom root and a h2 element inside it
      const shadow = document.getElementById("host").attachShadow({ mode: "open" });
      const shadowEl = document.createElement("h2");
      shadowEl.textContent = "Hello from the shadow DOM";
      shadow.appendChild(shadowEl);
      const shadowDomStyleSheet = new CSSStyleSheet();
      shadowDomStyleSheet.insertRule("h2 { color: tomato; background-color: gold;}");
      shadow.adoptedStyleSheets = [shadowDomStyleSheet];
    };
  </script>
  <style>
    span { }
  </style>
</head>
<body>
  <div id="target"> the ocean </div>
  <div id="host"></div>
</body>
</html>