chromium/content/test/data/input_box.html

<!DOCTYPE html>
<html>
<head>
  <style>
    body, html {
      width: 100%;
      height: 100%;
      margin: 0;
    }

    #space {
      width: 10000px;
      height: 10000px;
    }

    #input {
      position: absolute;
      top: 4000px;
      left: 3000px;
      border:0;
      padding:0;
    }
  </style>
  <script>
    notifyBrowser = false;
    function notifyWhenLoaded() {
      if (loaded)
        window.domAutomationController.send("LOADED");
      else
        window.notifyBrowser = true;
    }

    function rectAsString(rect) {
      return `${rect.x},${rect.y},${rect.width},${rect.height}`;
    }


    window.addEventListener('load', () => {
      document.getElementById("input").focus({'preventScroll': true});
      window.scrollTo(0, 0);

      window.loaded = true;
      if (window.notifyBrowser)
        notifyWhenLoaded();
    });
  </script>
</head>
<body>
  <div id="space"></div>
  <input id="input" type="text">
</body>
</html>