#include <QMainWindow>
#include <QApplication>
#include <QDockWidget>
#include <QLabel>

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

    w.setCentralWidget( new QWidget() );
    w.centralWidget()->setStyleSheet("background-color: green");

    QDockWidget* dock = new QDockWidget();
    dock->setWidget( new QLabel("Hello World",dock) );

    // make docking bar transparent!
    dock->setAttribute(Qt::WA_TranslucentBackground);
    dock->setAttribute(Qt::WA_NoSystemBackground);
    w.addDockWidget(Qt::BottomDockWidgetArea,dock, Qt::Horizontal);

    w.show();

    return a.exec();
}