The way wxBU_EXACTFIT is implemented in commit c1bb80987f
("Improve implementation of wxBU_EXACTFIT style for wxButton under wxGTK2",
2020-04-12) is too intrusive and disrupts button's appearance in some
themes. It should work better with themes if we reduce inner border in
a more GTK-compliant way by applying a dedicated GTK style to the button.
Closes#19081.
9a29ea6e63