Customizing QGroupBox
Let us look at an example that moves the QGroupBox's title to the center.

  QGroupBox {
      background-color: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
                                        stop: 0 #E0E0E0, stop: 1 #FFFFFF);
      border: 2px solid gray;
      border-radius: 5px;
      margin-top: 1ex; /* leave space at the top for the title */
  }

  QGroupBox::title {
      subcontrol-origin: margin;
      subcontrol-position: top center; /* position at the top center */
      padding: 0 3px;
      background-color: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
                                        stop: 0 #FF0ECE, stop: 1 #FFFFFF);
  }

class CDeviceWidget : public QGroupBox
{
Q_OBJECT
public:
    CDeviceWidget(QWidget *parent = 0);
};

CDeviceWidget::CDeviceWidget(QWidget *parent) : QGroupBox(parent)
{
    setTitle("Вычислительный модуль");
    setStyleSheet( "QGroupBox { border: 1px solid #8f8f91; }");
}

setStyleSheet( "QGroupBox { border: 1px solid #8f8f91; }");: