JSFiddle - React, Tailwind, and code Playground

CSS

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JavaScript

Date.daysBetween = function( date1, date2 ) {
  //Get 1 day in milliseconds
  var one_day=1000*60*60*24;

  // Convert both dates to milliseconds
  var date1_ms = date1.getTime();
  var date2_ms = date2.getTime();

  // Calculate the difference in milliseconds
  var difference_ms = date2_ms - date1_ms;
    
  // Convert back to days and return
  return Math.round(difference_ms/one_day); 
}

//Set the two dates
var bac  = new Date(2017, 5, 20); 
var today= new Date();

//displays 726
console.log( 'Days since ' 
           + bac.toLocaleDateString() + ': ' 
           + Date.daysBetween(today, bac));