I was trying to change the background color of the login screen for the gnome desktop manager on Ubuntu 20 but i've made a mistake and now have a error on the login screen with the message 'Oh no! Something has gone wrong.' and now i'm unable to log in as usual. Is there any way to regenerate the original login screen file or somewhere to get another?

All of the resources i found for changing the theme spoke about changing `lockDialogGroup` in `/usr/share/gnome-shell/theme/ubuntu.css`, but i didn't have that on my version of Ubuntu.
I was changing the hex values of `lockDialogGroup` in `/usr/share/gnome-shell/theme/Yaru/gnome-shell-theme.gresource` and then the error started occurring. I've used a tty shell to make sure the values are all ok but I must have entered a random character somewhere accidentally causing the error.

thanks in advance.