index.html

<!doctype html>
<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="refresh" content="0;url=demo/" />
        <title>highcharts-chart</title>
    </head>
    <body>
        <!--
            Visit demo/index.html to see live examples of your element running.
            This page will automatically redirect you there when run in the browser
            with `polymer serve`.
        -->
        <script>window.location = "demo/"</script>
    </body>
</html>