JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li class="current">Home</li>
    <li>About</li>
</ul>

CSS

ul{list-style:none;}
li{display:block; float:left; margin-right:10px; background-color:red; padding:10px;}
li.current{background-color:#78c4dd;}
li.current:after{
    border-left: 10px solid transparent;
    border-right: 11px solid transparent; content:"";
	border-top: 13px solid red;
    margin-top:15px;
}