spire.xls怎么画斜线边框

Spire.Xls.Workbook workbook = new Spire.Xls.Workbook();
workbook.LoadFromFile(@".\excle\text.xlsx");
Worksheet sheet = workbook.Worksheets[0];

IBorders border = sheet["E11"].Borders;
border[BordersLineType.DiagonalDown].LineStyle =LineStyleType.Thin;
border[BordersLineType.DiagonalDown].Color = Color.Black;