public BorderCollection Borders {get;}

var workbook = Workbook.Create( "test.xlsx" )

// Get first worksheet.
var worksheet = workbook.Worksheets[ 0 ];

// Set cells content.
worksheet.Cells[ "B15" ].Value = 0.1;

worksheet.Cells[ "C15" ].Value = 0.22;
worksheet.Cells[ "B16" ].Value = 0.31;
worksheet.Cells[ "C16" ].Value = 0.5;
worksheet.Cells[ "B17" ].Value = 0.36;
worksheet.Cells[ "C17" ].Value = 0.25;

// Get CellRange from B15 to C17 and modify the Borders of the 6 cells.
var cellRange = worksheet.Cells[ "B15", "C17" ];
cellRange.Style.Borders.SetInside( LineStyle.Medium, Color.DarkGreen );
cellRange.Style.Borders.SetOutline( LineStyle.Medium, Color.DarkGreen );

// Save workbook to disk.
workbook.Save();