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="expand()">
 expand year
</button>
<div id="pivot-container"></div>

SASS

.fm-cols-sheet .fm-cell[class*='fm-level-'], .fm-cols-sheet .fm-cell[class^='fm-level-'] 
    &:not(:nth-last-child(1)):not(:nth-last-child(2)):not(.fm-total-c) 
        min-width: 100px !important
        width: 100px !important
        background-color: green

.fm-data-sheet .fm-cell[class*='fm-level-']:not(.fm-total-c) 
    min-width: 100px !important
    width: 100px !important

    &.editable 
        padding: 0 !important
        z-index: 1 !important
        width: 120px

        input 
            width: 100%
            height: 100%
            font-size: inherit !important
            font-family: inherit !important
            background-color: transparent
            border: 0px solid
            box-sizing: border-box !important
            padding-right: 8px !important
            text-align: right !important

JavaScript

new Flexmonster({
  container: "#pivot-container",
  componentFolder: "https://cdn.flexmonster.com/",
  width: "100%",
  height: 600,
  toolbar: true,
  report: getReport()
});

function expand() {
	flexmonster.expandData('Year')
}

function getReport() {
	return {
    dataSource: {
        type: "json",
        data: [
        {
    ScenarioKey: 1,
    ScenarioName: 'Actual',
    OrganizationKey: 3,
    OrganizationName: 'Northeast Division',
    AccountKey: 80,
    AccountDescription: 'Building Leasehold',
    Amount: 586,
    Year: '2010',
    Month: '12'
  },
  {
    ScenarioKey: 2,
    ScenarioName: 'Budget',
    OrganizationKey: 3,
    OrganizationName: 'Northeast Division',
    AccountKey: 80,
    AccountDescription: 'Building Leasehold',
    Amount: 550,
    Year: '2010',
    Month: '12'
  },
  {
    ScenarioKey: 2,
    ScenarioName: 'Budget',
    OrganizationKey: 3,
    OrganizationName: 'Northeast Division',
    AccountKey: 81,
    AccountDescription: 'Vehicles',
    Amount: 380,
    Year: '2010',
    Month: '12'
  },
  {
    ScenarioKey: 1,
    ScenarioName: 'Actual',
    OrganizationKey: 3,
    OrganizationName: 'Northeast Division',
    AccountKey: 81,
    AccountDescription: 'Vehicles',
    Amount: 363,
    Year: '2010',
    Month: '12'
  },
  {
    ScenarioKey: 1,
    ScenarioName: 'Actual',
    OrganizationKey: 3,
    OrganizationName: 'Northeast Division',
    AccountKey: 82,
    AccountDescription: 'Equipment',
    Amount: 35,
    Year: '2010',
    Month: '12'
  },
  {
    ScenarioKey: 2,
    ScenarioName: 'Budget',
    OrganizationKey: 3,
    OrganizationName: 'Northeast Division',
    AccountKey: 82,
    AccountDescription: 'Equipment',
    Amount: 40,
    Year: '2010',
    Month: '12'
  },
  {
    ScenarioKey: 2,
    ScenarioName: 'Budget',
    OrganizationKey: 3,
    OrganizationName: 'Northeast Division',
    AccountKey: 83,
    AccountDescription: 'Furniture and Fixtures',
    Amount: 100,
    Year: '2010',
    Month: '12'
  },
  {
   ...