JSFiddle - React, Tailwind, and code Playground

HTML

<nav>
    <ul>
        <li onclick="show(this)">Item 1</li>
        <li onclick="show(this)">Item 2</li>
        <li onclick="show(this)">Item 3</li>
    </ul>
</nav>

CSS

nav li {
    width: 100px;
    background: #DDD;
    margin: 10px;
}
nav li:hover,
nav li.selected {
    width:150px;
    background: coral;
}

JavaScript

var selected = document.getElementsByClassName('selected');
function show(obj) {
    if (selected.length) selected[0].className = '';
    obj.className = "selected";
}