QWidget background color does not fully cover the QWidget

Using Qt Creator, I have set a QWidget's background property to black. However, some parts of the QWidget, more specifically, between QFrames/QGroupBox开发者_StackOverflow社区es are still in its system's default color.

Now, I thought that the QFrames and QGroupBoxes need to have its background property set to black too, but it did not work. I have also tried setting the border-color to black, but it does not work, since by default borders, margins are set to 0.

QWidget { background: black; }

Any advice on this issue?

EDIT

The QWidgets are placed in QMdiArea. However, if I make it a QWindow, it works. However, I want the QWidgets to be in the QMdiArea. Also, if I just show the QWidgets as it is, the spaces that I have mentioned above are transparent.

It sounds like you have some widgets within another widget, and are setting the contained widgets to be black, but then the space between them is not black. If that is the case, it is likely because you have a layout in the containing widget, which allocates space between each contained widget. The empty space between widgets will be drawn with the containing widget's background color.

Found out the solution. It seems that you need to set the background color at the QMdiSubWindow, not at QWidget. Don't know why, but it seems logical.