We experienced a bug in the our Beta 1 theming mechanism for the predefined window's Alert, Prompt and Confirm dialogs. This is why, in the Beta 2 release that should be available by the end of this week, you can change the themes of RadWindow and Alert by simply using the Theme
parameter in the static method RadWindow.Alert. The theme parameter represents just an url that points to a resource xaml file which contains the themes of BOTH RadWindow and Alert.
the Telerik team
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