Oxygen is the default KDE theme engine and it has very interesting customizing capabilities. Oxygen has some interesting options that can be used to customize its appearance and create a very interesting look.
What follows is my approach in tweaking the Oxygen appearance to my liking. Enjoy!
In the screenshot below you can see the final result; take into consideration that the look can change depending on what kind of color scheme is applied.
In my case I am using the Evolvere color scheme; you can install it from here: http://kde-look.org/content/show.php/Evolvere+color+scheme?content=164101