Sorry - the link in the text is an HTML file ... it turns out that Github's idea of an HTML file is their page showing you the HTML source. So you actually have to copy and paste it into a text file and save to desktop to use it. Unless there's some feature/setting I missed, which is more likely than not.

Meanwhile, I think you should be able to run the demonstrator for real at https://jsfiddle.net/Lke6p3dq/ - which, with some hint to apply the suffix to JSFiddle, can be described as myrtle fame jail totally