A style model implementation that is applied to objects within a user interface to define any attributes of the objects. The model is divided into two parts: a “runtime” which uses a style definition to affect the look and feel of the user interface, and a “design-time” which is the experience presented by WYSIWYG tools used to define the look and feel of the user interface. The design-time may be implemented in terms of the run-time objects. Properties associated with the styles can be set on the objects using the design-time UI and enforced at runtime. Styles may be grouped into themes to provide an easy mechanism to apply changes to many objects.