/usr/share/ubuntu-mate/settings-overlay/ is in ubuntu-mate-default-settings 18.04.17.
This file is owned by root:root, with mode 0o755.
..
/usr/share/ubuntu-mate/settings-overlay/config/
/usr/share/ubuntu-mate/settings-overlay/config/Trolltech.conf
/usr/share/ubuntu-mate/settings-overlay/config/folder-color/
/usr/share/ubuntu-mate/settings-overlay/config/folder-color/hide_donation
/usr/share/ubuntu-mate/settings-overlay/config/plank/
/usr/share/ubuntu-mate/settings-overlay/config/plank/dock1/
/usr/share/ubuntu-mate/settings-overlay/config/plank/dock1/launchers/
/usr/share/ubuntu-mate/settings-overlay/config/plank/dock1/launchers/caja.dockitem
/usr/share/ubuntu-mate/settings-overlay/config/plank/dock1/launchers/clock.dockitem
/usr/share/ubuntu-mate/settings-overlay/config/plank/dock1/launchers/desktop.dockitem
/usr/share/ubuntu-mate/settings-overlay/config/plank/dock1/launchers/firefox.dockitem
/usr/share/ubuntu-mate/settings-overlay/config/plank/dock1/launchers/matecc.dockitem
/usr/share/ubuntu-mate/settings-overlay/config/smplayer/
/usr/share/ubuntu-mate/settings-overlay/config/smplayer/smplayer.ini
/usr/share/ubuntu-mate/settings-overlay/config/tilda/
/usr/share/ubuntu-mate/settings-overlay/config/tilda/config_0