JSFiddle - React, Tailwind, and code Playground
HTML
<ul class="test">
<li class="one">adasdasd
<li class="one">asdasdsad
<li class="one">asdasdsad
<li class="two">asdasdsad
<li class="two">asdasdasdas
</ul>
CSS
ul.test .one:last-child {color:red;}
JavaScript
var n = $('.one').length;
$('.one').eq(n-1).css('color', 'red');