JSFiddle - React, Tailwind, and code Playground

HTML

<div class="items">
    <article class="today">
        this is today
    </article>
    <article class="today">
        this is today
    </article>
    <article class="today">
        this is today
    </article>
    <article>
        this is today
    </article>
    <article>
        this is today
    </article>
  
</div>

CSS

article {
    background: cyan;
}

.black { 
    background: black;
    color: white;
}

JavaScript

$( "article.today:last" ).addClass('black');