this post is useful to me.

To change the gtk look on gnome 3/gnome 2 hybrid as in debian 6 you must use the command line.

Apparently Gnome is reading the gtk.css file setting. So you need to substitute the gtk-dark.css to the gtk.css:

cd /usr/share/themes/Adwaita/gtk-3.0

cp gtk.css gtk.css.orig

cp gtk-dark.css gtk.css