JSFiddle - React, Tailwind, and code Playground

HTML

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

JavaScript

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

    dayRender: function (date, cell) {
        
        var today = new Date();
        var end = new Date();
        end.setDate(today.getDate()+7);
        
        if (date.getDate() === today.getDate()) {
            cell.css("background-color", "red");
        }
        
        var start = new Date();
        start.setDate(today.getDate()+1);
        
        
        while(start <= end){
            
          //alert(start + "\n" + tomorrow);
            if(start.getDate() == date.getDate()){
                cell.css("background-color", "yellow");
            }
    
           var newDate = start.setDate(start.getDate() + 1);
           start = new Date(newDate);
        }        
    }   
});