To reproduce: ThemeResolutionService.ApplicationThemeName = "FluentDark"; this.documentTabStrip1.TabStripAlignment = Telerik.WinControls.UI.TabStripAlignment.Left; this.documentTabStrip1.TabStripTextOrientation = Telerik.WinControls.UI.TabStripTextOrientation.Vertical; Workaround: this.documentTabStrip1.TabStripElement.ItemBorderAndFillOrientation = Telerik.WinControls.UI.PageViewContentOrientation.Horizontal;