DataTables Excel Export - Customize Border & Background Color for Merged Headers

hjwoo

Question:
I am using DataTables to export data to Excel and customizing the exported file using the customize function in excelHtml5. I want to apply a border and background color to all cells, including merged headers (complex headers), but the border and background color do not appear on the merged header cells.

url: https://live.datatables.net/repepazu/1/edit
code:

new DataTable('#example', {
    layout: {
        topStart: {
            buttons: ['copyHtml5',   
                   {
                    extend: 'excelHtml5',
                    customize: function (xlsx) {
                      var sheet = xlsx.xl.worksheets['sheet1.xml'];
                      var mergeCells = $('mergeCells', sheet);
                      mergeCells[0].appendChild(_createNode(sheet, 'mergeCell', {attr: { ref: ['B2:C2'] }}));
                      mergeCells[0].appendChild(_createNode(sheet, 'mergeCell', {attr: { ref: ['D2:F2'] }}));
                      mergeCells[0].appendChild(_createNode(sheet, 'mergeCell', {attr: { ref: ['B3:D3'] }}));
                      mergeCells[0].appendChild(_createNode(sheet, 'mergeCell', {attr: { ref: ['E3:F3'] }}));
                      
                      mergeCells[0].appendChild(_createNode(sheet, 'mergeCell', {attr: { ref: ['A2:A3'] }}));
                        
                      $('row[r=1] c', sheet).attr('s', '47');
                      $('row[r=2] c', sheet).attr('s', '47');
                      $('row[r=3] c', sheet).attr('s', '47');
                      function _createNode(doc, nodeName, opts) {
                          var tempNode = doc.createElement(nodeName);
                          if (opts) {
                            if (opts.attr) {
                              $(tempNode).attr(opts.attr);
                            }

                            if (opts.children) {
                              $.each(opts.children, function(key, value) {
                                tempNode.appendChild(value);
                              });
                            }

                            if (opts.text !== null && opts.text !== undefined) {
                              tempNode.appendChild(doc.createTextNode(opts.text));
                            }
                          }

                          return tempNode;
                        }
                      
                        // Selector to add a border
                         sheet.querySelectorAll('row c').forEach((el) => {
                           el.setAttribute('s', '25');
                         });
                    }
                }, 
                'csvHtml5', 'pdfHtml5']
        }
    }
});