$ gsettings set org.gnome.desktop.interface gtk-theme 'Adwaita'
Fantastic, thank you so much
Yesterday I was not having time for this (please write down your Librem 5 current outputs, so you can go back to them, not to give up 
):
gsettings get org.gnome.desktop.interface gtk-theme
gsettings get org.gnome.desktop.interface icon-theme
gsettings get org.gnome.desktop.wm.preferences theme
Please install (might be the missing/necessary application, but not sure any more):
apt list gnome-themes-extra-data −− should be already installed
sudo apt update
sudo apt install gnome-themes-extra
Make changes that you prefer:
gsettings set org.gnome.desktop.interface gtk-theme "Adwaita-dark"
gsettings set org.gnome.desktop.interface icon-theme 'Adwaita'
My current UI setup shows that above works on Librem 5:
sudo apt install materia-gtk-themegsettings set org.gnome.desktop.interface gtk-theme 'Materia-dark-compact'
If intended to be used (as screenshot shows, for demonstration purpose here only), but there is no need for already installed icons change, IMO (and there are few other compatible icons available as well, as I already linked above):
sudo apt install obsidian-icon-theme
gsettings set org.gnome.desktop.interface icon-theme 'Obsidian'
Sorry for not understanding, what outputs are you referring to? My old eyes like the look of the results!
But as an absolute novice working in the PureOS environment I need step-by-step instructions to be able to accomplish this feat.
So if you are up to it? Highly appreciated.
So far thank you for your input. 
This part of the first three Linux commands from my post will give (get) you output (it will not change anything) or tell you which gtk-theme or icon-theme are you using now/currently (in order to go back or restore the one you like better):
The part you wrote
sudo apt update
sudo apt install gnome- themes-extra
This in case the (gnome themes extra data) is not installed?
It comes pre installed on the phone.
apt list ... will show you which package is or needs to be installed (sudo apt install ...):
apt list gnome-themes-extra-data
apt list gnome-themes-extra
And if not used until now:
sudo apt update −− will connect your Librem 5 to PureOS repository,
sudo apt upgrade −− will upgrade your PureOS installation with the latest packages.
“I made the changes I prefer” but the results are the same black screen with white text. The other default apps stay with the same white background.
Looks like back to square one.
Thank you
I hope I am not mistaken by thinking that the dark mode would change all the default apps?
When I get my nerve back I will try again🤨
In the meantime thank you for your effort’s.
You might have to reboot after making the changes to see the full effect.
That I did, No changes.
For me it needs to written down in sequence.
Do this, do that….
For new users to the PuriOS it is a very bumpy road.
It will take the time, that’s why I initially requested step by step tutorials. Still think that for the basic installing of Purism related apps there could be made more of an effort. Having said that… there are some good people in the forum that help out and do their best.
But the problem is that the same people “swim” in those matters and sometimes hard for them to grasp that you are not there yet. Hence the incomplete back and forth.
Thank you for your input Gavauden.
Hello, I have installed Millipixels but it crashes at start with Bizantum version. Could you please confirm that it is OK for you ? Not having a Camera app is a problem for me (QR code scanning, etc.)
Thank you !
Millipixels is working fine for me. Make sure you have the kill switch for the camera/microphone not enabled.
Thank you quarnero, I succeeded to change it to dark mode. How can I make it a black black background.
I changed my background to “vantablack” with a picture. Is it possible to change the Adwaita-dark to vantablack using the pic?
Thank you very much for your patience and help.
No it still does not work I have uninstalled Millipixels and I hope to reinstall it and make it work but I am not sure
Regarding docks, I’ve tried a Dell K17A dock, that’s an older USB-C dock that has VGA, HDMI, and mini-DP connectors. With that the Librem5 doesn’t recognise the HDMI. With a modern cheap USB-C dock from eBay it gives HDMI. Some comments suggest that lack of support is due to Librem5 not supporting Thunderbolt and requiring DP passthrough, but I have all my laptops configured to disable Thunderbolt and they all work with it. Some newer Dell docks have worked, but no-one has given me one for free and they are unreasonably expensive.
Use the pine64 dock