JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://dl.dropboxusercontent.com/s/y4enc3buyzz2m3a/fullcalendar.css">
<script src="https://dl.dropboxusercontent.com/s/93dskqt37q1caxr/fullcalendar.min.js"></script>
<div id='calendar'></div>

CSS

.cellBg {
    background: #000;
    color: #fff;
}

JavaScript

var $calendar = $('#calendar').fullCalendar({
    header: {
        left: 'prev,next today',
        center: 'title',
        right: 'month,basicWeek,basicDay'
    },
    
    defaultView: 'month',

    dayRender: function (date, cell) {
         //Month is zero-based, so, 9 is october
         var holiday_date = new Date(2014,9,20);
         var date_as_locale = date.toLocaleDateString();
         if (date_as_locale == holiday_date.toLocaleDateString()) {
            cell.css("background-color", "red");
         }
         holiday_date = new Date(2014,9,27);
         if (date_as_locale == holiday_date.toLocaleDateString()) {
             cell.css("background-color", "red");
         }
         var day_of_the_week = date.getDay();
         if ((day_of_the_week == 0) || (day_of_the_week == 6)){
             cell.css("background-color", "red");
         }
    }
});