Visually indicate when the form buttons get focus

[aaron-collier]

Why was this change made? 🤔

Refs #3170 - this adds a visual indication when a button has gained focus using tab navigation.

WGAG Recommendation:

Ensure that when actionable elements receive focus, that it appears on screen and that a visible focus
indicator is present. Focus can be indicated in different ways, including change of background, lightness,
border, outline, underline, and other visual methods. Avoid the use of the "outline: none" CSS property.
As of WCAG 2.1, a custom focus indicator should have a minimum contrast ratio of 3:1 against the background.

How was this change tested? 🤨

⚡ ⚠ If this change involves consuming from or writing to another service (or shared file system), run integration test create_object_h2_spec.rb and/or test manually in [stage|qa] environment, in addition to specs. ⚡

Does your change introduce accessibility violations? 🩺

⚡ ⚠ Please ensure this change does not introduce accessibility violations (at the WCAG A or AA conformance levels); if it does, include a rationale. See the Infrastructure accessibility guide for more detail. ⚡

[aaron-collier]

Note: this allows the auto-citation slider to gain tab focus.