Zukitwo is an open source and totally free GTK+ theme designed especially for the GNOME desktop environment. It works with the latest version of GNOME, which includes the GNOME Shell user interface, and supports all GNU/Linux operating systems.
Installing the GTK3 theme
To install the GTK3 version of the theme on your desktop environment, begin by downloading the latest release from Softpedia or the project’s website (see link at the end of the article) save it on your Home directory, and extract its contents using an archive manager utility.
Open the file manager, right click on an empty area on your Home directory, and select the "Create New Folder" option to create a new folder, which will you will rename it as .themes (yes, with the dot in front of the name, as the folder will be hidden automatically by the system).
To view hidden files and folders, use the “View hidden files” entry on the main menu of your file manager or press the CTRL+H keys on your keyboard. Open the extracted directory and copy the Zukitwo folder to the .themes folder.
Then, open your Control Center application, go to the "Themes" section, and select the theme from there. Zukitwo will be applied in real time, but if it doesn’t or you see some display issues with various applications, simply restart your computer.
Installing the GTK2 theme
To install the GTK2 version of the Zukitwo theme, right click on your desktop, select the “Change Desktop Background” option, click on the Theme tab, then drag and drop the theme's archive in the Appearance Preferences window.
If everything is OK, you will receive a confirmation message and you can activate the theme just by clicking on it. Please note that these instructions are available for version 2 of the GNOME desktop environment.