Add Series Lines
Add a series lines and format to color green, 3 points wide and cap type flat.
Output: SeriesLinesFormat.xlsx
var workbook = new Workbook();
var worksheet = workbook.Worksheets[0];
worksheet.GetRange("J1:L1").SetValue(new[] { "Series 1", "Series 2", "Series 3" });
worksheet.GetRange("I2:I5").SetValue(new[] { "Point 1", "Point 2", "Point 3", "Point 4" });
worksheet.GetRange("J2:J5").SetValue(new[] { 2, 4, 6, 8 });
worksheet.GetRange("K2:K5").SetValue(new[] { 4, 3, 2, 1 });
worksheet.GetRange("L2:L5").SetValue(new[] { 2, 1, -1, -2 });
var chart1 = worksheet.Charts.Add<BarChart>("A1");
chart1.ChartType = ChartType.Column;
chart1.Size.HeightInches = 2.5;
chart1.Size.WidthInches = 3.5;
chart1.DataSource = "Sheet1!$I$1:$L$5";
chart1.Grouping = BarGrouping.Stacked;
chart1.SeriesOverlap = 1;
chart1.SeriesLines = new SeriesLines();
chart1.SeriesLines.Line.Color = Color.Green;
chart1.SeriesLines.Line.WidthPoints = 3;
chart1.SeriesLines.Line.CapType = LineCap.Flat;
workbook.SaveAs("SeriesLinesFormat.xlsx");