/usr/share/themes/ is in gtk2-engines 1:2.20.2-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/themes/Clearlooks/
/usr/share/themes/Clearlooks/gtk-2.0/
/usr/share/themes/Clearlooks/gtk-2.0/gtkrc
/usr/share/themes/Crux/
/usr/share/themes/Crux/gtk-2.0/
/usr/share/themes/Crux/gtk-2.0/gtkrc
/usr/share/themes/Industrial/
/usr/share/themes/Industrial/gtk-2.0/
/usr/share/themes/Industrial/gtk-2.0/gtkrc
/usr/share/themes/Mist/
/usr/share/themes/Mist/gtk-2.0/
/usr/share/themes/Mist/gtk-2.0/gtkrc
/usr/share/themes/Redmond/
/usr/share/themes/Redmond/gtk-2.0/
/usr/share/themes/Redmond/gtk-2.0/gtkrc
/usr/share/themes/ThinIce/
/usr/share/themes/ThinIce/gtk-2.0/
/usr/share/themes/ThinIce/gtk-2.0/gtkrc