Install kde-style-breeze-qt4 by entering the following commands in the terminal:
sudo apt update sudo apt install kde-style-breeze-qt4
Description:
Widget style for Qt 4 and KDE Software
This is the default widget style for KDE's Plasma desktop. This build has the plugin for with Qt 4. . This package is part of the Breeze theme module.
Homepage: https://projects.kde.org/projects/kde/workspace/breeze
Version: 4:5.12.4-0ubuntu1
Section: universe/kde