JSFiddle - React, Tailwind, and code Playground

HTML

<nav class="tabs">
    <ul>
        <a href=""><li>Cloud</li></a>
        <a href=""><li>Cloud</li></a>
        <a href=""><li>Cloud</li></a>
        <a href=""><li>Cloud</li></a>
    </ul>
</nav>

CSS

nav.tabs {
    /* generic wrapper for the sidebar tabs */
}

ul {
    list-style: none;
}

ul a {
    text-decoration: none;
}

ul li {
    position: relative;
    max-width: 189px;
    display: block;
    background: #0083b8;
    border-bottom: 1px solid #9cbec4;
    color: #fff;
    text-decoration: none;
    padding: 15px;
}

ul li:hover:after {
	right: 100%;
	border: solid transparent;
	content: " ";
	height: 0;
	width: 0;
	position: absolute;
	pointer-events: none;
}

ul li:hover:after {
	border-color: rgba(0, 0, 0, 0);
	border-left-color: #000000;
	border-width: 15px;
	top: 50%;
	margin-top: -15px;
}