[Datepicker component] Set focus outline color on calendar button

[imagoiq]

Datepicker component is missing a style for the calendar icon button (and inside the overlay) on focus and uses the default style from the browser.

On Firefox

On Chrome

[davidritter-dotcom]

I could add the focus color for the calendar icon button and for the days inside but unfortunately I couldn't find where firefox adds its focus styles for the navigation buttons.

[imagoiq]

I could add the focus color for the calendar icon button and for the days inside but unfortunately I couldn't find where firefox adds its focus styles for the navigation buttons.

It works with something like that:

button.ngb-dp-arrow-btn:focus-visible {
  outline: forms.$input-focus-outline-thickness solid var(--post-contrast-color);
}