Install xfce4-panel-dev by entering the following commands in the terminal:
sudo apt update sudo apt install xfce4-panel-dev
Description:
Xfce4 panel development files
In this package, you can find the development files distributed with the Xfce4 panel, the main panel of Xfce4 desktop environment. The files in this package are mainly going to be of interest for you if you intend to code applications which use some of the Xfce4 C panel functions.
Homepage: http://www.xfce.org/
Version: 4.12.2-1ubuntu1
Section: universe/devel