These elements are perfect for your web application. Carefully crafted, they can be easily customized through the layer effects or have their shape altered, since they are all vectorial shapes in color or gradient layers. There are a lot of different styles for action buttons, combo menus, and back/forward elements. The idea with this is that you can have a quick start for theming your interface elements, simply altering one layer effect and propagating through the rest. You can even add a colouring layer and change its colour to change the overall colour of the entire set.