Dynamic Panel-width in AbsoluteLayout


I have a AbsoluteLayout, in it a Panel. I want that the Panel gets dynamically sized by the browser window…
The root AbsoluteLayout should have max width from Browser and the Panel the max width in the root Layout.

If i set the absolute Layout to 100 % width, dont see anything… Whats wrong? I read in Vaadin Book if i want to use Percentage in a Component the Parent Component must have a defined Size. But how i do it?