Themes are a powerful addition to the ASP.NET framework. By taking advantage of themes, we can dramatically reduce the amount of content that we need to add to individual ASP.NET pages. Themes enable us to define the appearance of a control once and apply the appearance throughout a Web application. Therefore, themes enable us to easily create Web sites that have a consistent and maintainable design.  This improves the maintainability of our site and avoids unnecessary duplication of code for shared styles.