Background color not displayed

I am unable to see background in xlsm file.

**I have imported these libraries**
xlsx = require('xlsx'),
fileSaver = require('file-saver');

**I am using the following code**

**for setting the background**
cell = {t:'n' , v: workSheet['A' + (row+1)].v + workSheet['B' + (row+1)].v , f:'A' + (row+1)+'+'+'B'+(row+1) ,s: {bgColor: { indexed: 64 }}};

**and this for writing into file**
wbout = xlsx.write(wb, {bookType:'xlsx', bookSST:true, type: 'base64',cellStyles:'true'});

// to blob
function sheet_to_blob (s) {
const buf = new ArrayBuffer(s.length)
const view = new Uint8Array(buf)
for ( var i = 0; i != s.length; ++i ) view[i] = s.charCodeAt(i) & 0xFF
return buf
}
// export xlsx with file-saver
fileSaver.saveAs(new Blob([sheet_to_blob(wbout)], {
type: 'application/octet-stream'
}), 'test.xlsx')

**and it says ReferenceError: Blob is not defined**