JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr><td class="comment">Foo</td></tr>
</table>

CSS

* { margin: 0; padding: 0;}
td { border: 1px solid black; }
.comment:after {
    content: "";
    position: relative;
    top: 0.5em;
    border-left: 0.5em solid transparent;
    border-top: 0.5em solid red;
}