Hi Richard,
Thank you for your interest in Syncfusion Products.
You can use Syncfusion Window control to achieve this. Please refer below online sample to get more details on this issue:
http://samples.syncfusion.com/ASPNET/7.1.0.30/web/tools.web/samples/3.5/NotificationPackage/Window/CoreFeature/cs/corefeature.aspxPlease try this and let me know if this helps.
Regards,
Melba