[focusgroup] create a default visual indicator?

[travisleithead]

It has been expressed in accessibility discussions (990 and aria-1947) that providing a visual indicator for a focusgroup could be helpful even for sighted users as a clear pattern to know that a group can be navigated with arrow keys.

Perhaps there is room for a new user agent default stylesheet CSS pseudo class? E.g.,

   [focusgroup]:focus-within {
        /* ua-default visual styles */
    }

[travisleithead]

Note, in Issue #990, additional support for a visual indicator was mentioned:

Visual indicator seems valuable for the whole focusgroup area (@keithamus, @scottaohara). See also a demo by Ryan Mulligan: https://codepen.io/hexagoncircle/pen/QWMZBve

[github-actions]

There hasn't been any discussion on this issue for a while, so we're marking it as stale. If you choose to kick off the discussion again, we'll remove the 'stale' label.