index.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>&lt;x-dialog&gt;</title>

    <script src="components/platform/platform.js"></script>

    <link rel="import" href="components/src/x-dialog.html">
</head>
<body>

<x-dialog draggable resizable title="This is my title!">
    This is my content
</x-dialog>

<script>
    window.addEventListener('polymer-ready',function(){
        var dialog = document.querySelector('x-dialog');
        dialog.show();
    })
</script>

</body>
</html>