JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://code.jquery.com/ui/1.8.18/themes/base/jquery-ui.css" type="text/css" media="all" />
<input id=calender>

CSS

.mybold>a.ui-state-default {
    font-weight:bold;
    background-color: yellow ; 
    background-image: none ;
}

JavaScript

var events = {};
events[new Date('04/14/2012')] = new Event('Valentines Day', 'mybold');
events[new Date('04/18/2012')] = new Event('Payday', 'mybold');
    $('#calender').datepicker({
        changeMonth : true,
        changeYear : true,
        beforeShowDay : function(date) {
            var event = events[date];
            if (event) {
                return [ true, 'mybold', event.text ];
            } else {
                return [ true, '', '' ];
            }
        }
    });