this.radSyntaxEditor1.SyntaxEditorElement.EditorFontFamily = new Telerik.WinControls.SyntaxEditor.UI.FontFamily("Cascadia Code");
this.radSyntaxEditor1.SyntaxEditorElement.EditorFontSize = 13;

   at Telerik.WinControls.TelerikPaintHelper.GenerateSnapShotWithBitBlt(Control control)
   at Telerik.WinControls.UI.RadWaitingBar.AddBackgroundImageToAssociatedControlCoverPanel()
   at Telerik.WinControls.UI.RadWaitingBar.ShowCover()
   at Telerik.WinControls.UI.RadWaitingBar.StartWaiting()
   at TelerikWinFormsApp1.RadForm1.radButton1_Click(Object sender, EventArgs e) in C:\Projects\1564934_telerikwinformsapp1\TelerikWinFormsApp1\RadForm1.cs:line 31

        public class CustomWaitingBar : RadWaitingBar
        {
            protected override void AddBackgroundImageToAssociatedControlCoverPanel()
            {
                Size associatedControlSize = this.AssociatedControl.Size;
                if (associatedControlSize.Width <= 0 || associatedControlSize.Height <= 0)
                {
                    return;
                }

                Bitmap controlImage = new Bitmap(associatedControlSize.Width, associatedControlSize.Height);
                this.AssociatedControl.DrawToBitmap(controlImage, new Rectangle(Point.Empty, associatedControlSize));
                SolidBrush semiTransBrush = new SolidBrush(this.AssociatedControlCoverPanel.BackColor); // Color.FromArgb(128, 255, 255, 255) Default color
                Graphics g = Graphics.FromImage(controlImage);
                g.FillRectangle(semiTransBrush, new Rectangle(Point.Empty, controlImage.Size));
                this.AssociatedControlCoverPanel.BackgroundImage = controlImage;
            }

            public override string ThemeClassName
            {
                get
                {
                    return typeof(RadWaitingBar).FullName;
                }
            }
        }

    Private Sub RadButton2_Click(sender As Object, e As EventArgs) Handles RadButton2.Click
        Dim spreadExporter As GridViewSpreadExport = New GridViewSpreadExport(gvAssetSchedule)
        AddHandler spreadExporter.CellFormatting, AddressOf spreadExporter_CellFormatting
        Dim exportRenderer As New SpreadExportRenderer()
        spreadExporter.ExportVisualSettings = True
        Dim filename = "..\..\export" & DateTime.Now.ToLongTimeString().Replace(":", "_") & ".xlsx"
        spreadExporter.RunExport(filename, exportRenderer)
        Process.Start(filename)
    End Sub

    Private Sub spreadExporter_CellFormatting(sender As Object, e As Telerik.WinControls.Export.CellFormattingEventArgs)
        If e.GridCellInfo Is Nothing Then
            Dim selection As CellSelection = e.CellSelection
            Dim range As CellRange = selection.CellRanges(0)
            Dim val = selection.Worksheet.Cells(range.FromIndex.RowIndex, range.FromIndex.ColumnIndex).GetValue()
            Dim format As New CellValueFormat("@")
            selection.Worksheet.Cells(range.FromIndex.RowIndex, range.FromIndex.ColumnIndex).SetFormat(format)
            Dim dt As New DateTime(1900, 1, 1)
            Dim parsedDays = 0
            If Integer.TryParse(val.Value.RawValue, parsedDays) Then
                dt = dt.AddDays(parsedDays)
                selection.Worksheet.Cells(range.FromIndex.RowIndex, range.FromIndex.ColumnIndex).SetValue(dt.Year & "-" & MonthName(dt.Month))
            End If
        End If
    End Sub

StyleDefinition normalStyle = this.radRichTextEditor1.Document.StyleRepository[RadDocumentDefaultStyles.NormalWebStyleName];
normalStyle.ParagraphProperties.SpacingAfter = 20;
normalStyle.ParagraphProperties.SpacingBefore = 20;