debian wiki: GDM

  1. Edit /etc/gdm3/greeter.dconf-defaults as root
  2. Uncomment and/or modify the desired settings
  3. Save and close the editor
  4. Finally, run as root: dpkg-reconfigure gdm3

片段示例，其中icon-theme那行需手动添加

/etc/gdm3/greeter.dconf-defaults
---

#  - Change the GTK+ theme
[org/gnome/desktop/interface]
gtk-theme='Arc-Darker'
icon-theme='Arc'
cursor-theme='Breeze'