An Introduction to the Raspbian Desktop - Learning Raspbian - page 53

Openbox Configuration Manager
Openbox is the default Windows manager that is bundled with Raspbian. A
Windows manager is responsible for the placement and appearance of Windows
in a desktop environment.
You can also customize your desktop using Openbox Configuration Manager ,
which is found in Preferences .
The Openbox Configuration Manager
You can install any themes designed for Openbox on your Raspberry Pi. There are
many different themes preinstalled that you can choose from, or you can download
many themes from the Internet. One such website that you can download themes
from is http://box-look.org/ .
Examples of the different Openbox themes