Consider exposing a ThemeBuilder template for the Popup component.
https://www.telerik.com/kendo-react-ui/components/popup/
https://docs.telerik.com/kendo-ui/controls/popup/overview
https://docs.telerik.com/blazor-ui/components/popup/overview
https://www.telerik.com/kendo-angular-ui/components/popup/
https://github.com/telerik/kendo-themes/blob/develop/tests/popup/popup-no-data.html