cuStomizing the uSer interface In this section we describe how to modify the appearance of our Flex applications. First, we need some theoretical knowledge to get acquainted with terms like theme, skin, and style. We describe the difference between families of components (from the Flex 3 and Flex 4 libraries) and the ways of changing instances or classes of elements. Then we will dig deeper into the process of skinning by using Flash Builder and other tools of the Adobe suite like