How do I set or change specific style sheet properties in Qt for a QWidget, without resetting the whole style sheet?

Question

I've been searching for a while for an answer to this problem and I'm rather surprised that I have not found a solution. I'm working with Qt on Mac and would like to customize QPushbuttons and other QWidgets, but I want to maintain the native look somewhat as well. For example, if I want to remove the margins of a QButton using style sheets, I do:

QPushButton btn(this);
...
btn.setStyleSheet("margin:0;");

This indeed removes the margins, but it also removes the native style already set for default buttons. Of course, I just want to modify margins using style sheets, how do I do this?

Also, I would expect that btn.styleSheet() would return the native style sheet, but it is blank by default. Only when I set my own style sheet, does it return a valid value, but only for the property I set. I get that setStyleSheet would reset the style sheet, but how do I modify certain properties and leave everything else as is?

Answer 1

TL;DR: It can't be done that way.

The native style cannot be generally expressed as a CSS style sheet, thus styleSheet() is empty by default on all styles. Thus, unfortunately, it's not possible to change native style elements one-by-one, since typically they are drawn by the platform APIs that allow little if any customization.

For examples, a QPushButton is drawn by the native calls on both OS X and Windows.

In the specific case of the margin, though, you can easily work around by creating a proxy style that returns smaller control rectangle and crops and transforms the painter before passing it to the base style. This also works for colorization/color substitution etc. You basically have to accept that the base style has to do the drawing, and then it's up to you to tweak it.