Is there a way to make Ubuntu 18.04 login screen dark themed?

I'm on Ubuntu 18.04 using Communitheme, managed to make it dark within the desktop environment; the Nautilus is dark, the menus are all dark and browsers are also respectively dark themed. Everything looks great EXCEPT for the Login Screen which is white.

It's the window where you enter your password when you login. That window is white as opposed to the rest of the setup.

How do I go about making it black or dark or not-so-bright-white?

Edit (09/09/2019):

It's a success but there is still some white on the first screen (before you click enter and see the Password: field). And I need to change the text colour to white in contrast to the dark background.

Edit 2 (09/09/2019):

The second screen is completely sorted. This is the bit I was talking about -- the background is still bright. I'd like to make it the same colour as its surrounding which is dark.

Be Careful while editing the gdm3.css or its original file.. small mistakes in code.. will not let you login.. you need special support to bring back things to normal.. Proceed with your own.

1. Take backup of the file /usr/share/gnome-shell/theme/communitheme/gnome-shell.css

2. Open the file with gedit

   sudo -H gedit /usr/share/gnome-shell/theme/communitheme/gnome-shell.css
   

   Look for the fields below

   .login-dialog {
     border: none;
     background-color: transparent; }
     .login-dialog > StBoxLayout {
       background-color: green;
       border: 1px solid #cccccc;
       box-shadow: 0 3px 9px 1px rgba(0, 0, 0, 0.5);
       border-radius: 6px;
       padding: 12px 40px 24px 40px; }
   

   Change green to any valid color as you wish in the above field

   .login-dialog-user-list {
     spacing: 12px;
     padding: .2em;
     width: 23em; }
     .login-dialog-user-list:expanded .login-dialog-user-list-item:selected {
       background-color: blue;
       color: #ffffff; }
     .login-dialog-user-list:expanded .login-dialog-user-list-item:logged-in {
       border-right: 2px solid #E95420; }
   

   Change blue to any valid color as you wish in the above field.

3. Save the file, close & reboot to see the change in action.

   

Edit 09/09/2019

.login-dialog-username,
.user-widget-label {
  color: magenta;
  font-size: 120%;
  font-weight: bold;
  text-align: left;
  padding-left: 15px; }

and

.login-dialog-prompt-label {
  color: blue;
  font-size: 110%;
  padding-top: 1em; }