Defining the Border Radius
With the 2024 Q3 (18.2.24.806) release of Telerik Reporting, the border radius of the WPF Report Viewer's borders can be modified from the code behind or the XAML:
public MainWindow()
{
this.InitializeComponent();
this.ReportViewer1.CornerRadius = new CornerRadius(15);
}
<tr:ReportViewer.ReportSource>
<telerikReporting:UriReportSource Uri="..\..\..\..\..\..\..\Report Designer\Examples\Report Catalog.trdp" />
</tr:ReportViewer.ReportSource>
<tr:ReportViewer.Style>
<Style TargetType="tr:ReportViewer" BasedOn="{StaticResource {x:Type tr:ReportViewer}}">
<Setter Property="CornerRadius" Value="5"/>
<Setter Property="Padding" Value="5"/>
<Setter Property="BorderThickness" Value="3"/>
<Setter Property="BorderBrush" Value="Yellow"/>
</Style>
</tr:ReportViewer.Style>
</tr:ReportViewer>
Supported in all of the themes available to the WPF Report Viewer.