The standard widget-based GUIs that desktop systems tend to use do not lend themselves that readily to customization. As a result, you are generally faced with having to either override the painting function in a QWidget instance and handle every single pixel of the widget drawing, or to use stylesheet-based customization.

Qt stylesheets allow you to tweak the look and feel of individual widgets, even dynamically. They are essentially written using Cascading Style Sheet (CSS) syntax as used with HTML pages. They allow you to change elements of a widget, such as the borders, rounding corners, or the thickness and color of the elements.