Kubuntu and the Plasma Desktop is one of the most customizable Desktops. You can truly make Plasma to look and feel the way you like to work and play.
We will start our customization process with system setting. This is where you can make all the changes to your system.
Start by clicking on the Global Theme. This where you can set up your desired Theme for the system.
You can change to the existing ones or click on get new themes to download more themes.
You can also change your Desktop Style with Plasma Style.
In the Application style your can change the look and feel of your Windows.
In this Section by clicking on the Gnome/GTK Application you can change the way GTK Applications like Evolution would look on your KDE Plasma desktop.
In this section you can also change your windows decorations as well
By clicking the Titlebar Buttons you can change the location of the Window buttons or the order of them. Just drag the buttons around or add buttons by dragging them to the Title Bar.
In the Workspace Behavior section you can change the desktop effects, and create virtual desktops.
As I mentioned above KDE Plasma has loads of settings to make the desktop look and feel yours.