Berlin takes care of the user interface by itself without calling upon the use of GUI toolkits to render buttons, menus, and scrollbars. This way, all widgets in the applications on the desktop look alike. Eventually Berlin will support theming which will be truly universal theming. An often wanted feature of XFree86 has been support for true alpha transparency. But real alpha transparency has yet to be added.
Berlin has alpha transparency today.
Notice that everything can be seen behind a transparent window, not just the background image. Furthermore, Berlin's archicture allows for anything to be transparent, from a single widget to the entire desktop. The state of the art for graphical enviroments is pretty much pixel-based. Then the user changes the size of the fonts used for text so that he or she can read everything clearly. Berlin supports arbitrary linear transformations of the desktop.