Hi David,
Thank you for contacting us.
You need to theme CollapsibleHeaderPanelElement. Please have a look at the attached video (drag and drop over the browser to play) demonstrating you how to do it.
I hope this will help. Do not hesitate to write back with further questions.
Regards,
Ralitsa
Telerik
Check out Telerik Analytics, the service which allows developers to discover app usage patterns, analyze user data, log exceptions, solve problems and profile application performance at run time.
Watch the videos and start improving your app based on facts, not hunches.