How to add skins/themes/styles to a Qt application

Today I continued working on my ffmpeg wrapper application, after I get bored I tried to make something more interesting and I wanted to make the user able to change the theme of the application.

First I read the example from here  ,then i downloaded the widgetgallery files and added to my project and remove the entries of the norwegian style(created I that example).I am running on kubuntu and i have access to some basics themes but I do not know if the windows user can access them. I will try this scenario after building the application on my windows virtual machine.