Until recently I was using the default environment when installing Ubuntu, that is Unity. I just install KDE using the command
sudo apt-get install kde-plasma-desktop. When I open programs such as Firefox, LibreOffice, etc., their menus look terrible.
I suspect it has something to do with GTK+, but I don't know how to solve the problem. Is there a package that has not been installed by running the command
sudo apt-get install kde-plasma-desktop?