Hence treat them like those, a bunch of special case styling removed, which also doesn't override selection mode buttons styling.
2de0699 Adwaita: titlebutton are flat image-buttons
gtk/resources/theme/Adwaita/_common.scss | 17 +-
gtk/resources/theme/Adwaita/gtk-contained-dark.css | 370 ++++++++++++++------
gtk/resources/theme/Adwaita/gtk-contained.css | 370 ++++++++++++++------
3 files changed, 535 insertions(+), 222 deletions(-)
Upstream: git.gnome.org