Trouble resizing QDockWidget buttons with style sheet

Hello,
I am making a Qt Widget based Ui for use on a tablet (playbook) so touch interaction is needed.
Using Qt 4.8.2.
The dockWidget buttons are too small to be used with touch as is so I am trying to make them larger as per the examples http://doc.qt.io/qt-4.8/http://qt-project.org/doc/qt-4.8/stylesheet-examples.html#customizing-qdockwidget but I am not having much luck. After applying the style the buttons appear smaller and the frames disapear?
I am applying the style code from main.cpp as follows:
Code:

viewer->setStyleSheet("QDockWidget::close-button, QDockWidget::float-button {background: white; padding: 0px; icon-size: 30px; width: 20px; height: 20px;}" "QMainWindow::separator {width: 16px;}");
Any advice here would be greatly appreciated, I have been playing around with this for hours with no joy. I can move the buttons position and change their colour but nothing I do makes them bigger.
Cheers,
Jon