If your community has multiple group themes, you can select the default for all groups and optionally disable the ability of group owners to change their themes.
Navigate to Administration > Groups and select the Themes tab:
Select or change the following options:
- Enable Themes - If enabled, allows users who own groups on your community to select a group theme from the those available.
- Enable Theme Configuration - If enabled, group owners can customize their group theme's options.
- Default Theme - The default theme applied to the group when a new group is created.
Click Save to apply your changes.