Accessibility: Tab highlight of rectangular buttons (Dataverse)

[adam3smith]

Tested manually.

Elements should provide clear visual feedback when they're selected by tabbing.
None of the rectangular blue bottons on DV provide clear feedback. E.g., here, the "Link" button is selected:

Harvard (Demo) does this by both color changes and blue frame (it's a bit inconsistent, the edit button just gets a color change):

On Drupal we do visible lines around

I think a frame (thick white?) might be the way to go (check how the "Comment/Update comment" button highlights here on github, e.g.) because switching color might be tricky contrast-wise, but open to other ideas.