Improve accessibility by clearly defining keyboard focus

[mgifford]

CKAN version
https://demo.ckan.org

Describe the bug
Users should clearly know where they are in the site. This is especially important for keyboard only users. This is described in some detail here in the Drupal issue queue:
https://www.drupal.org/project/drupal/issues/1993574

The easiest example to see in the wild is:
https://www.gov.uk/guidance/accessibility-requirements-for-public-sector-websites-and-apps

I mentioned this in this morning's meeting, but realized I hadn't made an issue.

Additional details
https://www.w3.org/WAI/WCAG22/Understanding/focus-appearance-enhanced
https://adrianroselli.com/2017/02/avoid-default-browser-focus-styles.html
https://dev.to/elizabethschafer/designing-button-focus-states-for-better-usability-gm2