figure out keyboard selection (tab) on file inputs

[ehanahamed]

right now, everything else has a nice hover state & a clear and visible outline when selected using keyboard navigation.

However file inputs don't have keyboard-navigation outlines and don't show their hover color when using the keyboard either (although hovering with mouse/touchscreen has correct styling). File inputs still function with keyboard navigation as intended, but there is no visual indicator that you used tab to select it.