JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://cdn.ckeditor.com/4.5.4/standard-all/ckeditor.js"></script>
<textarea id="editor1">
    <p><span class="myItalic">Lorem Ipsum</span></p>
</textarea>

JavaScript

CKEDITOR.addCss('.myItalic {font-style: italic;}');
		CKEDITOR.replace( 'editor1', {
			allowContent: true,
			extraAllowedContent : 'span(*)'
		} );