JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://rangy.googlecode.com/svn/trunk/currentrelease/rangy-core.js"></script>
<script src="http://rangy.googlecode.com/svn/trunk/currentrelease/rangy-cssclassapplier.js"></script>
<input type="button" unselectable="on" onmousedown="formatCode(); return false" value="Code">

<div contenteditable="true">Go and format this bit of code: var code = true; and be happy</div>

CSS

.code {
   background-color: #ccc;
   font-family: Courier New, monospace;
}

JavaScript

var codeApplier = rangy.createCssClassApplier("code");

window.formatCode = function() {
    codeApplier.applyToSelection();
}