public class Style : Xceed.Workbooks.NET.StyleBase<IReadonlyStyle>, IReadonlyStyle  

using( var doc = Workbook.Load( "test.xlsx") )
  {
    var worksheet = doc.Worksheets[ 0 ];        
    worksheet.Cells[ 1, 1 ].Value = 25.6;    // Sets “B2” Value.
    worksheet.Cells[ 1, 1 ].Style.CustomFormat = "$0.0000";    // Sets “B2” display format to show “$25.6000”.
    worksheet.Cells[ 2, 2 ].Value = new DateTime( 2021, 7, 1, 10, 22, 33 );  // Sets “C3” Value.
    worksheet.Cells[ 2, 2 ].Style.CustomFormat = "h:mm AM/PM";  // Sets “C3” display format to show “10:22 AM”.
    worksheet.Cells[ “D4” ].Value = 33.5;
    worksheet.Cells[ “D4” ].Style.PredefinedNumberFormatId = 2;  // Sets “D4” display format to “0.00” to show “33.50”.
    doc.Save();
  }