JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.1.1.js"></script>
<script src="https://code.jquery.com/ui/1.12.0/jquery-ui.js"></script>
<link rel="stylesheet" href="https://code.jquery.com/ui/1.12.1/themes/cupertino/jquery-ui.css">


<p>Date: <input id="datepicker" type="text"></p>

CSS

.myClass
{
  border:2px red solid !important;
}

JavaScript

$( "#datepicker" ).datepicker({
	beforeShowDay  : function(date) // element (input box), instance [datepicker object]
				{
					var today = new Date();
					var isToday = (today >= date);
          if(isToday) return [true, 'myClass', 'Some caption (if needed)']; 
          else return [true, '', '']; //default ... you can pass false to disable this date
         },
});