<head> <script>/*This line is causing the problem */</script> </head> <body> <h1 style='text-align: center;'>This IS an iframe</h1> </body>
the js errror is : Uncaught TypeError: Cannot read property 'appendChild' of null (you need to be in development mode). If you remove the line the error will not longer exist.
The simplified source code example: https://codepen.io/anon/pen/MdoLpq
I'm a bit lost here, any ideas or hints are welcomed.