Theming Gnome Shell
Is encouraged to not theme Gnome Shell; designers and developers of Gnome Shell try to provide the best experience with the default theme, and theming Gnome Shell can cause wrong behaviours. |
If you want to theme it anyway, you need gnome-tweak-tool which should be provided on your distribution. Install it:
Ubuntu/Debian and .deb systems
sudo apt-get install gnome-tweak-tool
Fedora
sudo dnf install gnome-tweak-tool
Then go to https://extensions.gnome.org/extension/19/user-themes/ with Firefox (it only works with Firefox) and install that extension named "user themes".
Download a theme from websites like http://gnome-look.org and put it on ~/.themes folder (you can use /usr/share/themes to use a theme system wide)
Open Tweak tool application you installed previously and in the Appearance tab select the themes you want.