JSFiddle - React, Tailwind, and code Playground

HTML

<div class="popup-wrapper">
    <div class="popup">
        <h2 class="popup__header">Header</h2>
        <p class="popup__text">Lorem ipsum dolor sit amet, consectetur adipisicing elit. Doloremque id iste, voluptates porro sapiente qui. Reprehenderit consequuntur nisi quas quis eligendi fugit sed aliquid, odit ipsa labore dignissimos, laboriosam similique.</p>
    </div>
</div>

CSS

html, body {
    height: 100%;
}

body {
    margin: 0;
}

.popup-wrapper {
    display: flex;
    min-height: 100%;
}

.popup {
    display: inline-block;
    width: 300px;
    margin: auto;
    padding: 20px;
    text-align: left;
    background-color: white;
    border-radius: 5px;
    box-shadow: 0 0 15px rgba(0, 0, 0, 0.2);
}

.popup__header {
    margin: 0;
    font: 36px/1 serif;
}

.popup__text {
    margin: 0;
    font: 15px/18px sans-serif;
}

.popup__header + .popup__text {
    margin-top: 15px;
}