Many elements in the Windows interface use perspective, highlighting, and shading to provide a three-dimensional appearance. This emphasizes function and provides real-world feedback to the user's actions. For example, command buttons have an appearance that provides the user with natural visual cues that help communicate their functionality and differentiate them from other types of information.
Windows bases its three-dimensional effects on a common theoretical light source, the conceptual direction that light would be coming from to produce the lighting and shadow effects used in the interface. The light source in Windows comes from the upper left.
When designing your own visual elements, be careful not to overdo the use of dimensionality. Avoid unnecessary nesting of visual elements and using three-dimensional effects for an element that is not interactive. Introduce only enough detail to provide useful visual cues and use designs that blend well with the system interface.