code: function parseStyles(content, xml) {
    if (!content) {
      return {}
    }
    // https://social.msdn.microsoft.com/Forums/sqlserver/en-US/708978af-b598-45c4-a598-d3518a5a09f0/howwhen-is-cellstylexfs-vs-cellxfs-applied-to-a-cell?forum=os_binaryfile
    // https://www.office-forums.com/threads/cellxfs-cellstylexfs.2163519/
    const doc = xml.createDocument(content)
    const baseStyles = xml.select(doc, null, '//a:styleSheet/a:cellStyleXfs/a:xf', namespaces).map(parseCellStyle);
    const numFmts = xml.select(doc, null, '//a:styleSheet/a:numFmts/a:numFmt', namespaces)
      .map(parseNumberFormatStyle)
      .reduce((formats, format) => {
        formats[format.id] = format
        return formats
      }, [])
  
    return xml.select(doc, null, '//a:styleSheet/a:cellXfs/a:xf', namespaces).map((xf) => {
      if (xf.hasAttribute('xfId')) {
        return {
          ...baseStyles[xf.xfId],
          ...parseCellStyle(xf, numFmts)
        }
      }
      return parseCellStyle(xf, numFmts)
    })
  }
docs: http://officeopenxml.com/SSstyles.php