JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title></title>
    <script type="text/javascript" charset="utf-8" src="bp-modal.min.js"></script>
    <link rel="stylesheet" href="modal.min.css" type="text/css" media="all" />
  </head>
  <body>
    <p data-modal="test" style="text-align:center">Click me!</p>
    <div class="modals" style="overflow: hidden;">
      <div id="test" class="modal modal-medium modal-closeable">
        <div class="modal-header">
          <h2>This is a Medium-Sized Modal</h2>
        </div>
        <div class="modal-content">
          <p>
            This modal includes the class <code>modal-closable</code> which adds
            the fancy close button at the top right.
          </p>
        </div>
      </div>
    </div>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
	This modal includes the class <br><br><br>
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	This modal includes...

CSS

.modals,
.modals *,
.modals *:before,
.modals *:after {
  box-sizing: border-box;
}

.modals {
  align-items: center;
  background-color: rgba(0, 0, 0, 0.7);
  bottom: 0;
  display: none;
  justify-content: center;
  left: 0;
  position: fixed;
  right: 0;
  top: 0;
  z-index: 999;
}

.modals-shown {
  display: flex;
}

.modal {
  background: #fff;
  border-radius: 3px;
  box-shadow: 0 0 8px rgba(0, 0, 0, 0.4);
  display: none;
  flex-direction: column;
  max-height: 90%;
  overflow: auto;
  position: relative;
  right: 0;
  width: 90%;
}

.modal-shown {
  display: flex;
}

.modal-header {
  border-bottom: 1px solid #ddd;
  flex-grow: 0;
  flex-shrink: 0;
  overflow: hidden;
  padding: 12px 22px;
  position: relative;
  width: 100%;
}
.modal-header h1,
.modal-header h2,
.modal-header h3,
.modal-header h4,
.modal-header h5 {
  margin: 0;
}

.modal-footer {
  border-top: 1px solid #ddd;
  overflow: hidden;
  padding: 16px;
}

.modal-content {
  padding: 16px 24px;
}

.modal-small {
  max-width: 400px;
}

.modal-medium {
  max-width: 600px;
}

.modal-scrollable .modal-content {
  overflow-y: auto;
}

.modal-close {
  background-image: url("img/close.svg");
  background-position: center center;
  background-repeat: no-repeat;
  background-size: 25px 25px;
  cursor: pointer;
  height: 35px;
  margin: 7px;
  opacity: 0.3;
  padding: 10px;
  position: absolute;
  right: 0;
  top: 0;
  width: 35px;
}
.modal-close:hover {
  background-color: #ddd;
  opacity: 0.5;
}

JavaScript

document.addEventListener("DOMContentLoaded",()=>{const t=document.getElementsByClassName("modals")[0];var e=document.querySelectorAll("[data-modal]"),s=t.getElementsByClassName("modal");const a={},o=()=>{Object.keys(a).forEach(e=>{a[e].element.classList.toggle("modal-shown",a[e].shown)});var e=Object.keys(a).filter(e=>a[e].shown).length;t.classList.toggle("modals-shown",0<e)};[...s].forEach(e=>{if(a[e.id]={shown:!1,element:e},e.addEventListener("click",e=>e.stopPropagation()),e.classList.contains("modal-closeable")){const t=document.createElement("div");t.classList.add("modal-close"),t.addEventListener("click",()=>{a[e.id].shown=!1,o()}),e.appendChild(t)}}),[...e].forEach(e=>{e.addEventListener("click",()=>{a[e.dataset.modal].shown=!0,o()})}),t.addEventListener("click",()=>{Object.keys(a).forEach(e=>{a[e].shown=!1,o()})}),o()});