How do I style a Qt Widget not its children with stylesheets?

Question

I have a:

class Box : public QWidget

and it has

this->setLayout(new QGridLayout(this));

I tried doin

Answer 1

To be more precise I could have used:

QWidget#idName {
    border: 1px solid grey;
}

or

Box {
    border: 1px solid grey;
}

The latter is easier, in my opinion, as it doesn't require the use of id names.

The main problem with why these weren't working though is because this is considered a custom widget and therefore needs a custom paint event:

 void Box::paintEvent(QPaintEvent *) {
     QStyleOption opt;
     opt.init(this);
     QPainter p(this);
     style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
 }

This was taken from: Qt Stylesheet for custom widget