How to reduce QToolBar height?

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Here's how it looks if I change toolbar height:

Both on the left and right QIcon size is 16. On the right (Query) the toolbar height is 18:

toolbar->setIconSize(QSize(16, 16));
toolbar->setMaximumHeight(18);
toolbar->setContentsMargins(0,0,0,0);

and it changes the icon size. In between the Query and Log, see how much space space that toolbar takes. How to adjust its size without affecting the icon size?