JSFiddle - React, Tailwind, and code Playground

HTML

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

JavaScript

$(function() {
    $("#datepicker").datepicker({
        beforeShow: function (input, inst) {
            setTimeout(function() {
                inst.dpDiv.find('a.ui-state-highlight').addClass('ui-state-highlight-xxx');
            }, 100);
        }
    });
});