When you define your screen, make it very large (like 200 by 220) in the screen attributes. Then when you place the custom container on the screen in the screen painter, make it nearly fill the entire screen. Then in the attributes of the custom container, mark the Vertical and Horizontal resizing and set a minimum number of lines and columns. Your container will then automatically resize to fill your screen. This is same technique you can use on Tab Strips in the screen painter.
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