What is the process behind making custom widgets (using Qt) that don't look...well...ugly?

I know it is fairly trivial to make a "custom widget" that has say, a listbox and a pushbutton slapped together into one, but how would I go about making something that looks more like this:

[QAnalogWidgets](http://www.qt-apps.org/content/show.php/AnalogWidgets?content=87780)

I have made some rough mock-ups that basically use a PNG background (that I made in Photoshop) with basic elements like QLabels placed on top of them, but I don't think this is how I should be doing it. I know that Qt supports CSS -- is this what people use to create widgets that actually look good? Do I need to be working in the paintEvent methods? OpenGL?

Trying to search for anything "custom widget qt" related is just giving me tons of info about how to import them into the Designer, etc -- so any leads would be appreciated.

Thanks!