You are going about it the wrong way. gwt-ext is long dead.
Current Choices - Pure GWT UiBinder , Pure GWT LayoutPanel, Sencha GXT, Vaadin.
Using AbsolutePanel for building entire screens are not recommended. To get screens working across multiple resolution you need to start here https://developers.google.com/web-toolkit/doc/latest/DevGuideUiPanels
Also ensure you understand the concepts related to LayoutPanel and RootLayoutPanel.