How to set QPdfView's viewport background color

I'm trying to set a QPdfView's viewport background color, but unlike QAbstractScrollArea (from which QPdfView's derived), using stylesheet does not work.

Here's how I tried to do that:

#include <QApplication>
#include <QPdfView>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QPdfView *pdfView = new QPdfView();

    pdfView->setMinimumSize(100,100);
    //I tried to set stylesheet in different ways, in multiple combinations
    //but none worked
    //pdfView->setStyleSheet("background: white");
    pdfView->setStyleSheet("QWidget{background: white;}");
    //pdfView->viewport()->setStyleSheet("background: white");

    pdfView->show();

    return a.exec();
}

Note: You need to to find and target PdfWidgets, so modify your CMakeLists.txt according the below, to be able to use QPdfView:

find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Widgets PdfWidgets)
find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Widgets PdfWidgets)

target_link_libraries(MyExperiments PRIVATE
     Qt${QT_VERSION_MAJOR}::Widgets
     Qt${QT_VERSION_MAJOR}::PdfWidgets)

Here's how it looks, viewport is grey, and you can see the white background of QPdfView on the borders:

I also tried to change the background color of viewport by overriding QAbstractScrollArea::paintEvent, and here's how:

void paintEvent(QPaintEvent *event)
{
    QPdfView::paintEvent(event);

    QPainter p(viewport());
    QRect rect = viewport()->rect();

    rect.adjust(-1,-1,0,0);
    p.setBrush(QBrush(QColor(0,0,100)));
    p.drawRect(rect);
}    

But that ended up painting over viewport, not changing its background color, so it covers open documents, because If I use a transparent color, I can see the document through it.

I'm open to either or other ways, but I'd like to avoid using paintEvent if possible.

If you look at QPdfView's source code of paintEvent, you'll notice QPalette::Dark being used to fill viewport, and based on that, you can change its background color without obscuring open documents as follows:

#include <QApplication>
#include <QPdfView>
#include <QPalette>

int main(int argc, char **argv) 
{
    QApplication app(argc, argv);
    
    QPdfView view;
    
    QPalette palette = view.palette();
    palette.setBrush(QPalette::Dark, QColor("lime"));
    
    view.setPalette(palette);    
    view.show();
    
    return app.exec();
}

Note: QPalette::Dark needs to be used, changes to painting the viewport will only occur if made through it.

Source: Qt Forum How to set QPdfView's viewport background color?

Credit: ChrisW67