Install gtk2-engines-aurora by entering the following commands in the terminal:
sudo apt update sudo apt install gtk2-engines-aurora
Description:
Aurora gtk+-2.0 theme engine
"Aurora" refers to the natural light displays in the sky in polar regions. This package contains the Aurora theme engine for the GTK+ toolkit, version 2.0. . GTK+ is a multi-platform toolkit for creating graphical user interfaces.
Homepage: http://www.gnome-look.org/content/show.php?content=56438
Version: 1.5.1-4
Section: universe/x11