16.04 - Changing the background of the login screen changes the design of the login screen

In 16.04, to change the background of the login screen, I followed the accepted answer at How do I change the login screen in Ubuntu 16.04+?, however, when I selected the new background, the theme of the background changed as in:

1) The text box for the password is now in the centre of the screen (instead of the middle-left).

2) The look of the login prompt is now changed to old-style rectangular gray background

3) The login grid has disappeared.

I undid all the changes, however even the original look and feel of the login prompt is totally gone.

Here is how it looks now:

Also, the lock screen has had no effect to these changes and remains original.

How do I get the login back to its original look and feel, like this?

I had a look at all the available answers, but all of them talk about previous versions of Ubuntu (not 16.04) and they dont work.

Any help is greatly appreciated.

Thanks,

Shubhanga.

I figured out what the problem was. The problem is with lightdm in the sense that it changes the design of the login screen into the old layout. I believe the correct method was to just follow the answer at How do I change the login screen in Ubuntu 16.04+? and follow the unity-greeter settings and not install lightdm-gtk-greeter-settings.

Also, once unity-greeter has been suitably configured, the following command had to be executed in the terminal.

sudo apt purge lightdm-gtk-greeter lightdm-gtk-greeter-settings