The package gnome-shell-extension-better-volume 0.0-git20170425.1a66fab-1 has been added to kali-rolling. It has been imported from Debian: https://tracker.debian.org/pkg/gnome-shell-extension-better-volume -- More information about gnome-shell-extension-better-volume: http://pkg.kali.org/pkg/gnome-shell-extension-better-volume