Navigation focus border is ugly and potentially over-used

Just been talking to ghenrick and he asked me about the new border around navigation tree items.

Some questions:

1. why is it so ugly?
2. why do we need it?
3. Can we get rid of it (even if just on mouse press)?
4. Where in the spec demands it?
5. Is it trying to meet AA, or AAA?

The relevant information that I've found for it is suitably vague (https://www.w3.org/TR/UNDERSTANDING-WCAG20/navigation-mechanisms-focus-visible.html) and suggests that it is AA and it comes under section 2.4.7:]

2.4.7 Focus Visible: Any keyboard operable user interface has a mode of operation where the keyboard focus indicator is visible. (Level AA)

IMO, this border is a step backwards in terms of usability and user experience. It's confusing to a majority of users, it's ugly, and it's likely to be removed by themes anyway.

Pinging johno, and damyon.