Ubuntu stores it’s GTK themes in a user directory located at ~/.themes, since installing a new theme should not require administrator access. This is great for adding your own themes, which you can do by draggin them into the theme manager window, but applications ran as the root user will appear awkward as they are not using this theme.
You can either copy your ~/.themes to /root/.themes, or create a symbolic link to them:
$ sudo ln -s ~/.themes /root/.themes
Now any themes you install will be applied to the root user, even if you install new ones.
