/usr/share/themes/Nightmare/ is in openbox 3.5.2-8+deb8u1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/themes/Nightmare-01/openbox-3/
/usr/share/themes/Nightmare-01/openbox-3/bullet.xbm
/usr/share/themes/Nightmare-01/openbox-3/close.xbm
/usr/share/themes/Nightmare-01/openbox-3/iconify.xbm
/usr/share/themes/Nightmare-01/openbox-3/max.xbm
/usr/share/themes/Nightmare-01/openbox-3/shade.xbm
/usr/share/themes/Nightmare-01/openbox-3/shade_toggled.xbm
/usr/share/themes/Nightmare-01/openbox-3/themerc
/usr/share/themes/Nightmare-02/openbox-3/
/usr/share/themes/Nightmare-02/openbox-3/bullet.xbm
/usr/share/themes/Nightmare-02/openbox-3/close.xbm
/usr/share/themes/Nightmare-02/openbox-3/iconify.xbm
/usr/share/themes/Nightmare-02/openbox-3/max.xbm
/usr/share/themes/Nightmare-02/openbox-3/shade.xbm
/usr/share/themes/Nightmare-02/openbox-3/shade_toggled.xbm
/usr/share/themes/Nightmare-02/openbox-3/themerc
/usr/share/themes/Nightmare-03/openbox-3/
/usr/share/themes/Nightmare-03/openbox-3/bullet.xbm
/usr/share/themes/Nightmare-03/openbox-3/close.xbm
/usr/share/themes/Nightmare-03/openbox-3/iconify.xbm
/usr/share/themes/Nightmare-03/openbox-3/max.xbm
/usr/share/themes/Nightmare-03/openbox-3/shade.xbm
/usr/share/themes/Nightmare-03/openbox-3/shade_toggled.xbm
/usr/share/themes/Nightmare-03/openbox-3/themerc
/usr/share/themes/Nightmare/openbox-3/
/usr/share/themes/Nightmare/openbox-3/bullet.xbm
/usr/share/themes/Nightmare/openbox-3/close.xbm
/usr/share/themes/Nightmare/openbox-3/iconify.xbm
/usr/share/themes/Nightmare/openbox-3/max.xbm
/usr/share/themes/Nightmare/openbox-3/shade.xbm
/usr/share/themes/Nightmare/openbox-3/shade_toggled.xbm
/usr/share/themes/Nightmare/openbox-3/themerc