I have an application consisting of a viewport with "fit" layout, which contains a tabpanel. In addition to this, I would like to add a button which floats at the top right of the viewport. (The purpose of this button is to open a kind of global configuration menu.) I know I could add a tool to the tabpanel, but this appears in a separate bar above the tabs, which takes up too much space, hence the reason I would like to float a button top-right, where there is free space within the confines of the tab panel (unless the window size gets too small to display all the tabs, but let's ignore that for now).

Can someone suggest a way to do this?