Install yuyo-gtk-theme by entering the following commands in the terminal:
sudo apt update sudo apt install yuyo-gtk-theme
Description:
Yuyo GTK2 and GTK3 Theme
Yuyo has light and dark variations and a flat style with crisp clean lines. It is the official theme for Ubuntu MATE.
Homepage: https://github.com/snwh/yuyo-gtk-theme
Version: 0.3
Section: universe/gnome