JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="menu">
    <li class="item"><a href="#">Link 1</a><div class="popup">This is popup number one</div></li>
    <li class="item"><a href="#">Link 2</a><div class="popup">This is popup number two. <br/> It has a line break inside.</div></li>
</ul>

<div style="clear:both"></div>

<p>
    Like a potato emerging from the shadows, the icy core of comet Tempel 1 looms into view in a new picture from NASA's Stardust spacecraft released Tuesday.
</p>

CSS

.item{
    float: left;
    background: #ffc;
    height: 2em;
    padding: 5px 15px 0;
    border: 1px solid #000;
}

.popup
{
    display: none;
    position: absolute;
    left: 0;
    top: 2em;
    width: 100%;
    margin-top: 17px; /* To compensate for parent block's padding */
    color: #fff;
    background: #f00;
}

.item:hover .popup
{
    display: block;
}