Changes to Ready-made Counter Styles doc

I've been applying some editorial changes to 
https://www.w3.org/TR/predefined-counter-styles/ to make it more useful 
to readers.  They include:
- an icon to allow the reader to copy the style in a single click
- examples of each style (including those that are defined in the CS spec)
- linking to MDN for information about support of the style in browsers

You can see what i have done so far at:
https://w3c.github.io/predefined-counter-styles/test.html

If you have any comments or suggestions, please send sooner rather than 
later.  I am aware that the sample display is problematic for a couple 
of styles that produce very long counters, such as cjk-tally-mark, and 
i'm considering options for handling that.

cheers,
ri