DialogCardPage Namespace

While using Dialog, the code snippets from Dialog component (radzen.com) I get a build error saying -"The type or namespace name 'DialogCardPage' could not be found (are you missing a using directive or an assembly reference?) [BlazorDemo]" Since there is no mention about which namespace to be added etc. I am clueless. Any help here is appreciated. Thanks.

Maybe the entire source code will help you: