JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="sf-menu" id="suckerfishnav"><li class="current_page_item"><a href="http://dev.harveys.co.uk/">Home</a></li><li class="page_item page-item-619"><a href="http://dev.harveys.co.uk/case-studies/" title="Case Studies">Case Studies</a></li>

<li class="page_item page-item-564"><a href="http://dev.harveys.co.uk/industrial/" title="Industrial">Industrial</a></li>
<li class="page_item page-item-2"><a href="http://dev.harveys.co.uk/about/" title="About">About</a></li>
<li class="page_item page-item-82"><a href="http://dev.harveys.co.uk/services/" title="Services">Services</a></li>
<li class="page_item page-item-84"><a href="http://dev.harveys.co.uk/inspections/" title="Inspections">Inspections</a></li>
<li class="page_item page-item-8"><a href="http://dev.harveys.co.uk/clients/" title="Clients">Clients</a></li>
<li class="page_item page-item-193"><a href="http://dev.harveys.co.uk/latest-news/" title="News">News</a></li>
<li class="page_item page-item-79"><a href="http://dev.harveys.co.uk/contact/" title="Contact">Contact</a></li>
</ul>

JavaScript

$(function(){

    $('ul#suckerfishnav li:first-child').css('background-color', 'red');


});