That change instructs GWT to load a new CSS template for the Dark or Chrome theme. Dark is a more significant change from the Standard theme. You might not notice the change from Standard to Chrome with the minimal amount of GWT components in use in the starter application. We need to point out another important setting in the file. GAEJ___ChapterThree'/> That line tells App Engine where the entry point for the application is located.
Beginning Java Google App Engine by Kyle Roche, Jeff Douglas