I tried to change the log in screen background of Ubuntu 19.10. I did the following modification in gdm3.css.
#lockDialogGroup {
background: url(file:///usr/share/backgrounds/thumb-1920-606500.jpg);
background-repeat: no-repeat;
background-size: cover;
background-position: center; }
And I am quiet satisfied with the result. Now I have several minor glitches too.
At first login System freezes for around 2 secs with a black screen then the pinkish noise-texture screen flashes then everything goes to normal.
Second problem is that during a login session whenever for the 1st time I lock the system using super+L, the login screen is set to the grey version of noise-texture.png. After logging in for all the next instance locking the system produces expected screen(my customized one i.e " url(file:///usr/share/backgrounds/thumb-1920-606500.jpg)) ".
How to get rid of these 2 problems?