JSFiddle - React, Tailwind, and code Playground

HTML

<div class="lightbox">
    <div class="lightbox-content">
        <div class="sample-content"></div>
    </div>
    <div id="close-lightbox">Close</div>
</div>

CSS

.lightbox{
    position: fixed;
    padding-bottom: 30px; /*for the close button*/
    background: grey;
    min-height:100%;
}

.lightbox-content {
    overflow: auto;
    height: 300px;
    background-color: grey;
}

.sample-content {
    height: 360px; /*higher than ligbox content to activate overflow*/
    background-color: indianred;
}

#close-lightbox {
    position: absolute;
    bottom: 5px;
    left: 30%;
}