Collapse without javascript
<p>I know how to collapse (display / hide) a div:</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>$('#nav').click(function() { $('#hello').toggleClass('hidden'); });</code></pre>
<pre class="snippet-code-css lang-css prettyprint-override"><code>.hidden { display: none; }</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"&gt;&lt;/script&gt;

&lt;div id="nav"&gt;NAV&lt;/div&gt;
&lt;div id="hello" class="hidden"&gt;Hello&lt;/div&gt;</code></pre>
</div>
</div>
</p>

<p><strong>Is it possible to do this without Javascript / jQuery?</strong></p>

<p><em>I've tried the main answer from <a href="https://stackoverflow.com/questions/31506684/expand-collapse-mobile-navbar-without-javascript">this question</a>, but it is not working, as detailed <a href="https://jsfiddle.net/2k9bb8hd/" rel="noreferrer">here</a>.</em></p>