SiteMaps XSL Training Exercise

Apologies for posting such a simple problem, but I am dipping
my toe into the world of XML stylesheets, and would very much
appreciate a little feedback, and maybe some help and/or inspiration...

Basically, I have taken an XML SiteMap, and written a simple stylesheet
to render it in a browser window. My attempt is documented at:

Firstly:
As I am learning, this is being used as a training exercise. As such, I am
trying to be as  pedantic and technically correct as possible.
Therefore, have
I got everything correct here? any omissions? Default settings should be
defined (and explained where necessary).

Secondly:
It works. Very simplistic, but it does the job.
However, I am wondering if there is anything more I can do to enhance the
'user experience', or to aid navigation. Any suggestions or ideas?