Hello, Henri,
The Visual Style Builder demo is starting on my side when I click on the Launge demo button in our Demo application. See the attached picture for your reference. Also we are not aware of other issues like this, maybe there is some problem on your end. Is it possible to restart the Demo app again and try to open the example with VSB?
I did not consider this as bug in our demo, hence I marked the status of this item as Declined.
More information about where to find our themes is available in the following forum post which you open on the same topic. Please see my answer here: Location of the .tssp files for Winforms in UI for WinForms | Telerik Forums
Regards,
Nadya | Tech Support Engineer
Progress Telerik
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