JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div id="openModal" class="modalDialog">
        <div>
            <a href="#close" title="Close" class="close">X</a>
            <h2>
                Modal Box</h2>
            <p>
                This is a sample modal box that can be created using the powers of CSS3.</p>
            <p>
                You could do a lot of things here like have a pop-up ad that shows when your website
                loads, or create a login/register form for users.</p>
        </div>
    </div>
</body>

CSS

.close:hover
{
    background: #00d9ff;
    cursor:pointer;
}
.modalDialog
{
    position: fixed;
    font-family: Arial, Helvetica, sans-serif;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    background: rgba(0,0,0,0.8);
    z-index: 99999;
    opacity: 0;
    -webkit-transition: opacity 400ms ease-in;
    -moz-transition: opacity 400ms ease-in;
    transition: opacity 400ms ease-in;
    pointer-events: none;
}

.modalDialog > div
{
    width: 400px;
    position: relative;
    margin: 10% auto;
    padding: 5px 20px 13px 20px;
    border-radius: 10px;
    background: #fff;
    background: -moz-linear-gradient(#fff, #999);
    background: -webkit-linear-gradient(#fff, #999);
    background: -o-linear-gradient(#fff, #999);
}
.close
{
    background: #606061;
    color: #FFFFFF;
    line-height: 25px;
    position: absolute;
    right: -12px;
    text-align: center;
    top: -10px;
    width: 24px;
    text-decoration: none;
    font-weight: bold;
    -webkit-border-radius: 12px;
    -moz-border-radius: 12px;
    border-radius: 12px;
    -moz-box-shadow: 1px 1px 3px #000;
    -webkit-box-shadow: 1px 1px 3px #000;
    box-shadow: 1px 1px 3px #000;
    z-index:10000000;
    pointer-events: all;
}

JavaScript

$(document).ready(function() {
    $("#openModal").fadeTo(500, 1);
    
    $('a.close').click(function() {
        $("#openModal").fadeTo(500, 0);
    });
});