JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tinymce/4.4.3/jquery.tinymce.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tinymce/4.4.3/tinymce.min.js"></script>
<div id="wrapper" style="height:1000px;background-color:red">
  <textarea></textarea>
</div>

CSS

#wrapper, .mce-tinymce,.mce-stack-layout, .mce-edit-area{
        display: flex!important;
        flex-direction: column;
        flex: 1;
        align-items:stretch;
      }
      .mce-tinymce iframe{
        flex: 1;
      }

JavaScript

$(document).ready(function(){
   tinymce.init({
     selector: 'textarea'
   });
 });