A GNOME Shell extension allowing the user to set the position, size and delay of the OSD windows for sound or luminosity. Also adds transparency.
The better option is to install it from https://extensions.gnome.org/extension/1345/better-osd/
How to manually install the extension ?
Download files and put them in an better-osd
folder to ~/.local/share/gnome-shell/extensions/
You may need to restart the gnome shell environnment ("logout and login again", or alt+f2 + r + enter).
The original OSD source code is around these lines: https://github.com/GNOME/gnome-shell/blob/master/js/ui/osdWindow.js#L194