Cfrgtkky

Good evening,

I'm trying to change some of the colours of my login screen in my Ubuntu 18.04. I followed some questions here on AskUbuntu, and edited my css files at /usr/share/gnome-shell/theme/gnome-shell.css (I'm using that configuration) - Specifically, I changed the values of .lockDialogGroup to a nicer dark gray.

My login screen is indeed now a nice dark gray instead of that hellish purple.

However, if I lock my computer without shutting down the machine, I still get a different purple gradient, which I haven't managed to change. I'm serching around but since I don't even know what to call this "behind-the-shield" screen, I can't find relevant results.

I suspect the login screen and the lock screen are two different managers altogether.

Here's a short mp4 video of me literally filming my screen, to make you understand which color I'm trying to change:

https://imgur.com/8aBWhd4

EDIT: There seems to be a discrepancy between my first-after-boot login screen, and my login-after-locking screen.

first Login screen after boot:

After-lock login screen:

"behind-the-shield" screen as you mentioned in question is called unlock screen.

this answer is provided only for desktop session "Ubuntu"

if you use, desktop-session other than Ubuntu which is the default one, the style sheet that is configured in /usr/share/gnome-shell/modes/ubuntu.json may not be used. instead they may use /usr/share/gnome-shell/gnome-shell-theme.gresource which is not covered in this answer.

Disclaimer: playing with shell theme files (.css files) is very dangerous, small mistakes will stop access to the desktop session. Only tty will work. i have several times reinstalled Ubuntu in such cases. although i have successfully changed login screen background and unlock screen background, Do this at your own risk.

when Ubuntu 18.04 is freshly installed,

the login screen background can be changed by editing /etc/alternatives/gdm3.css file. This file is a linked file to /usr/share/gnome-shell/theme/ubuntu.css

now i have changed my login-screen background-color to green by editing /etc/alternatives/gdm3.css file.

#lockDialogGroup {

  background: green url(resource:///org/gnome/shell/theme/noise-texture.png);

  background-repeat: repeat; }

by editing this file /etc/alternatives/gdm3.css, unlock screen background also changed to green because the linked file of /etc/alternatives/gdm3.css which is /usr/share/gnome-shell/theme/ubuntu.css is configured in the file /usr/share/gnome-shell/modes/ubuntu.json

{

    "parentMode": "user",

    "stylesheetName": "ubuntu.css",

    "enabledExtensions": ["ubuntu-dock@ubuntu.com", "ubuntu-appindicators@ubuntu.com"]

}

unlock screen background when it is set to "ubuntu.css" in ubuntu.json file

but i want my login screen background and unlock screen background to be different,

for this, copy /usr/share/gnome-shell/theme/ubuntu.css file and paste in the same folder and rename it like "my-unlock-screen.css"

edit /usr/share/gnome-shell/modes/ubuntu.json like below to use my-unlock-screen.css style sheet instead of ubuntu.css

{

    "parentMode": "user",

    "stylesheetName": "my-unlock-screen.css",

    "enabledExtensions": ["ubuntu-dock@ubuntu.com", "ubuntu-appindicators@ubuntu.com"]

}

now i edited /usr/share/gnome-shell/theme/my-unlock-screen.css like below

#lockDialogGroup {

  background: blue url(resource:///org/gnome/shell/theme/noise-texture.png);

  background-repeat: repeat; }

and now unlock screen background is blue.

here is the link to video showing login-screen and unlock-screen with green and blue colors. https://imgur.com/6mCjd8I