[ Thanks to kiterunner for this link.
]
“We saw the quiet evolution of GNOME Shell aka the next
generation GNOME desktop environment. Now lets do some GNOME Shell
theming. Hope you guys are familiar with Elementary and Ambiance
GTK themes. Now they have these stunning GNOME Shell variants which
are absolutely beautiful. First of all you need to download these
themes.* Before installing these themes, you have to be in your GNOME
Shell environment(obviously). [Ref: How to install GNOME Shell in
Ubuntu]How to Install GNOME Shell Themes?
* First of all, you need to backup your original GNOME Shell
Theme. Copy-paste /usr/share/gnome-shell/theme directory to your
Home folder”