Accessibility: Investigate use of `:focus-visible` for focus states

[daneah]

The problem

Focus states provide valuable feedback to keyboard users, low vision users, and more. However, they can be heavy-handed for cases where a user is already actively clicking on an element, as an example.

The solution

Use :focus-visible in judicious ways to make Pharos elements show the focus outline only when necessary.

Alternatives considered

Leaving the focus states as they are could be alright, but it provides unnecessary motion and can draw attention from the task at hand.

Additional information

See this article for a good overview.