Make sure tour toolbar button has :focus styling when tabbed to.

...bit OT and I don't know if there is an issue already filed for this, but are the Edit and Tour buttons "tied" with the toolbar? What about sites that don't use the toolbar (disabled because they use admin_menu for example) or sites that have mainly anonymous users (those don't see the toolbar by default) and still want to display a tour to their visitors?

Screenshots tabbing to tour button, matching the toolbar link's focus style.
:focus working with less selectors.

This addresses the focus problem that was identified! Unfortunately the tab order is incorrect. It should be visually as it appears:
Home Menu Shortcuts admin Tour

But instead the order is:
Home Menu Shortcuts Tour admin

That can probably be addressed by: #1913086: Generalize the overlay tabbing management into a utility library

But because Tour is visually a long ways from the other tabs it would be useful if on focus it stood out more.

@Bojhan are there any reasons not to do this from a UX perspective?

This patch fixes the problem.

I'd love to keep this issue focused (pun!) and solve related issues in their own tickets.

I prefer to have focus styling be more obvious than just an outline. Keyboard users have vision problems too.

That's a separate issue, so don't let that stop this one. :)

Just created a new issue here #1929010: Improve Contrast for onfocus Menu Items

Committed and pushed to 8.x. Thanks!