JSFiddle - React, Tailwind, and code Playground

HTML

<div class="pop"></div>

CSS

.pop {
    background:#333;
    width:250px;
    height:120px;
    border-radius:8px;
    display: inline-block;
}
.pop::before {
    content:"Pop up head";
    display: block;
    width: 90px;
    background:#333;
    border-radius:8px;
    padding: 3px;
    margin-top: -14px;
    text-align: center;
    color: white;
}