This is a GNOME-compatible pink GTK theme.
First, right-click on your desktop and then select "Change Desktop Background." After that, click on the first tab, which is "Theme." Next, drag and drop the theme's archive into the "Appearance Preferences" window. Finally, if everything goes correctly, you will receive a confirmation message, and you can activate the Bikkuri UI theme just by clicking on it.
GNOME is an international project that aims to create a complete desktop environment, the graphical user interface that sits on top of a computer operating system, entirely from free software. The project includes creating software development frameworks, selecting application software for the desktop, and working on the programs that manage application launching, file handling, and window and task management. GNOME is part of the GNU Project and can be used with various Unix-like operating systems, most notably Linux, and as part of Java Desktop System in Solaris.
The GNOME project emphasizes simplicity, usability, and making things "just work." The name, originally standing for GNU Network Object Model Environment, now stands as a symbol for creating a user-friendly, accessible desktop environment that is free and open to everyone.