JSFiddle - React, Tailwind, and code Playground

HTML

<a href="">About</a>

CSS

a {
    padding: 10px 20px;
    background: linear-gradient(to bottom, #ccc, #cf0);
    position: relative;
    font: 1em/1.2 Arial, sans-serif;
    color: #fff;
    text-decoration: none;
}

a:before {
    content: "";
    position: absolute;
    bottom: 0;
    left: 50%;
    margin-left: -5px;
    width: 0; 
    height: 0; 
    border-left: 5px solid transparent;
    border-right: 5px solid transparent;
    border-bottom: 5px solid #000;
}