JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.5.0/css/bootstrap-datepicker.standalone.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datepicker/1.5.0/js/bootstrap-datepicker.min.js"></script>
<input type="text" value="2015-12-22" data-date-format="yyyy-mm-dd">

CSS

.myClass {
  outline: dashed 1px red;
  background: orange !important;
  color: white !important;
}

JavaScript

var myDate = new Date('2015/12/25').toISOString();
var myText = 'Корпоратив! Вася опять нажрется!'

$('input').datepicker({
  beforeShowDay: function(date) {
    //console.log(date == myDate, date, myDate)
    if (date.toISOString() == myDate) {
      return { enabled: true, classes: 'myClass', tooltip: myText }
    }
  }
})