The Page.Theme property sets the name of the theme used for the page. If you want the settings on the page to take precedence over the settings in the theme, use the Page.StyleSheetTheme property. For more information, see ASP.NET Themes and Skins Overview.

The Page.Theme property must be set prior to the Page.PreInit event; setting the Page.Theme property after the Page.PreInit event will cause an InvalidOperationException exception.

The specified theme must exist as either an application or a global theme. If the theme does not exist, an System.Web.HttpException exception is thrown.