Well, Qt does not provide these capabilities. This means that you cannot easily use stylesheets for this purpose. However, there might be OS-specific ways to change the color of the title bar. On Windows (10 and later) you can use DwmSetWindowAttribute to enable dark mode for the title bar. Another way is to get a window without decoration/borders from the OS and then draw the entire title bar yourself using Qt. Then, you can also style the title bar using stylesheets. It might get a little complicated to draw the close and minimize buttons in the correct OS style yourself.
@aha_1980 Here's how I bootstrapped new working settings for QtCreator.
On Windows the settings reside in <user>\Appdata\Roaming\QtProject, which contains files QtCreator.db, QtCreator.ini and directory qtcreator with lots of subdirectories, xml files etc.
Renaming that directory then running QtCreator created a new settings directory (from a template kept in the Qt distro) . After that, QtCreator started behaving normally, though of course without any memory of previous projects or kit associations.
Copying the QtCreator.ini file from the renamed directory restored those memories but did not make the bad behavior come back.
Apparently the root problem is an incompatibility between Qt Creator 4.10.2 and some old file in the settings folder. In my case those files were created years ago by QtCreator 3.5. And since 3.5 does not even support VC 2015, I guess it was high time for a change.
I ran into the same problem, where a closed QDialog would magically appear over a QMainWindow when hovering over the programs' TaskBar icon...
I understand that QDialogs do not get shown in the TaskBar thumbnail, but how does the Dialog appear out of thin air, after dismissing it??
I have to open and close the external window before my QML gui is opened.
So I do this in my main before the QML engine loads the QML file.
Then I pass the necessary information from the external window via pointers to my GUI.
I did some exploratory debugging and found that (on Windows 10) QWindowsStyle::drawPrimitive() is not being called to render checkboxes, but rather they are being drawn with DrawThemeBackgroundEx() from uxstyle.dll (which I would have expected to support High DPI correctly.)
After looking at the screen shots attached to the ticket referenced above I discovered that I have a different sort of drawing problem; checkboxes are being render correctly, but at the same size (13px) regardless of device scaling.
On Windows 7 checkboxes appear to render correctly with device scaling enabled.