Promlems with setStyleSheet

Hi to all,
I'm doing some test with the style sheet. I'm trying to customize a QSlider.
I create a class inherited from QFrame containing just a QSlider so:

Code:

#ifndef __VOLWIDGET_H__
#define __VOLWIDGET_H__
 
#include <QFrame>
#include <QSlider>
 
class VolWidget : public QFrame
{
    Q_OBJECT
 
public:
    VolWidget( QWidget* parent );
    virtual ~VolWidget();
 
signals:
    void sig_volChanged(int);
 
protected:
 
private:
    QSlider* m_volSlider;
};
#endif // __VOLWIDGET_H__

After creating the QSlider in the ctor I would apply to it a style using the setStyleSheet routine.

Code:

VolWidget::VolWidget( QWidget* parent )
: QFrame(parent)
{
    setFrameStyle( QFrame::Panel | QFrame::Raised );
 
    setStyleSheet(" QSlider::groove:vertical { \
                    background: red; \
                    position: absolute; \
                    left: 4px; \
                    right: 4px; }\
                    QSlider::handle:vertical { \
                    height: 10px; \
                    background: green; \
                    margin: 0 -4px; /* expand outside the groove */ } \
                    QSlider::add-page:vertical { \
                    background: white; } \
                    QSlider::sub-page:vertical { \
                    background: pink; }");
 
    m_volSlider = new QSlider(Qt::Horizontal);
    m_volSlider->setMinimum( 0 );
    m_volSlider->setMaximum( 100 );
    m_volSlider->setValue( 100 );
 
    QVBoxLayout *vLayout = new QVBoxLayout();
    vLayout->setContentsMargins(0, 0, 0, 0);
    vLayout->addWidget(m_volSlider);
 
    setLayout(vLayout);
 
    connect(m_volSlider, SIGNAL( valueChanged(int) ), this, SIGNAL( sig_volChanged(int) ) );
}

In my case the code has no effect. No style sheet is applied to the QSlider.
Where I'm wrong?
Regards