style.TableProperties.Borders = new TableBorders(new Telerik.Windows.Documents.Model.Border(BorderStyle.Single, System.Windows.Media.Colors.Red));
style.TableCellProperties.Borders = new TableCellBorders(new Telerik.Windows.Documents.Model.Border(BorderStyle.Single, System.Windows.Media.Colors.Red));
More information on the topic you can find in the Styles help article.
Hope this is helpful.
Regards,
Tanya
Progress Telerik
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