Example of CSS inheritance in <use> elements, including over-riding visibility

With regards to Issue 32 in the Document Structure chapter [1]:

> Why is ‘visibility’ called out specially? It might be better just to
include an example that shows this.

And specifically, with regards to Action-3768 from today's meeting (when I
promised to come up with said example),
I present:

   - http://codepen.io/AmeliaBR/pen/ZYMEKM/?editors=110


If all is agreed that it effectively demonstrates the subject matter, I
will make create a stand-alone SVG version and description and push it to
the spec repository.

If it's too complicated for a spec example, I could try to make a version
that uses plain rectangles or ellipses, but I would be disappointed...

--AmeliaBR

[1]: https://svgwg.org/svg2-draft/struct.html#UseElement