JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.7.0/themes/base/jquery-ui.css">
    <input type="text" id="dp" />

CSS

.highlight { background-color: red }

JavaScript

$(function() {
    var nowDate = new Date();
    nowDate.setHours(0,0,0,0)
    var nowTime = nowDate.getTime();

    var dpFirstDay = 0; //what day is the first day of the week (0 = sunday, 1 = monday...)

    $("#dp").datepicker({
        firstDay: dpFirstDay,
        beforeShowDay: function(date) {
            var d = new Date(date);
            d.setDate( d.getDate() - (((d.getDay() - dpFirstDay)%7)+7)%7 );
            for (var i = 0; i < 7; i++) {
                if (d.getTime() == nowTime)
                    return [true, "highlight"];
                d.setDate(d.getDate() + 1);
            }
            return [true, ""];
        }
    }); 
});