A list of available themes is displayed in this dialog. Select a theme by clicking on an item in the list.
Use the button to download additional themes from the Internet or load a theme from file.
Since Plasma™ 5.6 it is no longer possible to edit and customize individual components or items in a theme.
The recommended tools to check, blend and test themes is the plasma-sdk package, the Theme Explorer specifically.
For more technical information visit this page.