Ubuntu – Remove app icon from title bar in GNOME in Ubuntu 18.04

• Download this zip(Numix Flatstudio Dark Theme): https://www.dropbox.com/s/hvq89fo7rojpr5h/Numix-flatsudio-dark.zip?dl=0 (I have made a few changes to this to match my shell theme)

• Open terminal and type this:

  sudo chown [username] /usr/share/themes && sudo chown [username] /usr/share/icons
  

  replacing [username] with your username.

• Unzip this downloaded zip into /usr/share/themes
• Download this zip(Shell Theme): https://www.dropbox.com/s/d8ynaj6jnsktln4/Ozon.zip?dl=0
• Unzip this downloaded zip into /usr/share/themes
• Download this zip(Icon Pack): https://www.dropbox.com/s/850tkeijmraskfk/Ultra-Flat-Orange.zip?dl=0
• Unzip this downloaded zip into /usr/share/icons
• Open Tweak tool. Turn off the Global Dark Theme. There will be Numix-flatstudio-dark under the Window and the GTK+ dropdown. Select those. Under the Shell Theme dropdown, there will be Ozon-shell-master. Select this also. Select Ultra-Flat-Orange in the Icons dropdown menu.
• Now you will have a global dark theme

I was able to add border to windows in Ubuntu 18.04 by doing the following:

nano ~/.config/gtk-3.0/gtk.css

Then add the following:

decoration {
    border: 3px solid gray;
    background: gray;
}

After saving the file, remember refresh gnome using this command:

setsid gnome-shell --replace

I found it works well for Ambiance. I like the border slightly thicker (3px) to make it a little easier to see in laptop running in 1920x1080 resolution.

EDIT:

To customize the active title bar background colors. (use :backdrop for inactive windows)

.titlebar {
    background: #0759EB;
}

.titlebar:backdrop  {
    background: #829EDF;
    color:white;
}