[DefaultMember("Item")]
public class BorderCollection : Xceed.Workbooks.NET.StyleBase<BorderCollection> 

using( var workbook = Workbook.Create( "AddBorder.xlsx" ) ) 
  { 
    // Gets the first Worksheet; a Workbook always contains at least 1 Worksheet. 
    var worksheet = workbook.Worksheets[ 0 ]; 

    // Gets the Border collection for Cell A2. 
    var borders = worksheet.Cells[ "A2" ].Style.Borders; 

    // Sets the color and style of the rightmost Border. 
    borders[ BorderType.Right ].Style = LineStyle.Thick; 
    borders[ BorderType.Right ].Color = Color.Red; 

    // Saves Workbook to disk; 
    workbook.Save(); 
  }