JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://s3.amazonaws.com/flexmonster/2.3/demo.css">
<script src="https://cdn.flexmonster.com/flexmonster.js"></script>

<button onclick="exportClassicForm()">
Export
</button>

<div id="pivotContainer"></div>

CSS

#fm-pivot-view .fm-cell.fm-header.fm-header-c {
  text-align: right;
}

JavaScript

var pivot = new Flexmonster({
  container: "pivotContainer",
  componentFolder: "https://cdn.flexmonster.com/",
  toolbar: false,
  report: {
    dataSource: {
      filename: "data/data.csv"
    },
    "slice": {
      "rows": [{
          "uniqueName": "Category"
        },
        {
          "uniqueName": "Country"
        },
        {
          "uniqueName": "Color"
        },
        {
          "uniqueName": "Business Type"
        }
      ],
      "columns": [{
          "uniqueName": "Destination"
        },
        {
          "uniqueName": "[Measures]"
        }
      ],
      "measures": [{
          "uniqueName": "Quantity",
          "aggregation": "sum"
        }
      ],
      "expands": {
        "expandAll": true
      }
    }
  }
});

flexmonster.on('reportcomplete', function() {
  var pivotView = document.getElementById("fm-pivot-view");
  var oneMoreColHeaderElement = document.createElement("div");
  oneMoreColHeaderElement.classList.add("fm-header-c");
  oneMoreColHeaderElement.style.display = "none";
  oneMoreColHeaderElement.style.textAlign = "center";
  pivotView.insertBefore(oneMoreColHeaderElement, pivotView.firstChild);
});

function exportClassicForm() {
  let container = document.querySelector("#pivotContainer");
  let initialWidth = container.getBoundingClientRect().width;
  container.style.width = ((pivot.gridColumnCount() - 1) * 110 + pivot.getRows().length * 110) + "px";
  pivot.setOptions({
    grid: {
      type: "classic"
    }
  });
  pivot.refresh();
  pivot.on("exportcomplete", () => {
    pivot.off("exportcomplete");
    pivot.setOptions({
      grid: {
        type: "compact"
      }
    });
    pivot.refresh();
    container.style.width = initialWidth + "px";
  });
  setTimeout(() => {
    pivot.exportTo("excel",{
      destinationType: "file",
      header: 'line 1\nline 2\nline 3',
      filename: "xx",
      showFilters: true
    });
  }, 0);
}