This theme for Gnome or MATE desktops will theme your GTK applications to look like the old CDE desktop: http://gnome-look.org/content/show.php/GTK2-notif2?content=18886. Get this one if you want a classic look for your desktop.
Download this theme here: https://dl.opendesktop.org/api/files/download/id/1460763624/18886-GTK2-notif2.tar.gz.