Great, it works.
A bit complicated process and the tutorial could be a bit clearer. For example, rather than referring the reader to another page which is longer than the styles tutorial itself:
For this to happen however, you need to save the extension document with programming rights.
and doesn’t show what exactly needs to be set in order for this particular example to work it should just show the actual steps.
By the way, I just created a blank page with a style object as an admin user and didn’t set any rights at all and it still works without setting any rights anywhere. When I go to Page Administration page not a single checkbox is ticked.
Also the description says to set Use this extension option to Always on this wiki, the screenshot shows Always on this page, and what I see in my instance is none of the above:
Maybe a little thing but adds to confusion.