<main>
  <h1>CSS Only Modal</h1>
   <h2 class="caveat">*with some JavaScript for accessibility</h2>
  <p> Lorem ipsum dolor, sit amet consectetur adipisicing elit. Quos, animi. Voluptatibus, architecto perferendis eos fugit dicta expedita cum incidunt, temporibus iure, officiis vitae. Officia nobis quibusdam repellendus voluptatem illum maxime?</p>
  <a class="modal-btn" href="#modal">Click here to open modal</a>
</main>

<section role="dialog" aria-labelledby="modal-title" aria-hidden="true" class="modal" id="modal">
  <a class="modal-overlay" aria-hidden="true" href="#" tabindex="-1"></a>

  <div class="modal-content">
    <a title="Close modal" aria-label="Close modal" href="#" class="modal-close">&times; </a>
    <h2 id="modal-title"> Hello there! </h2>
    <p>Quibusdam nulla velit dolores sed neque facere ut, tenetur fuga itaque? Nostrum in numquam sapiente iusto excepturi cum iure aspernatur quia soluta eum? Suscipit sunt dicta libero? Eos, necessitatibus dignissimos!</p>
    <p> Click the close button or anywhere outside the modal to close it.</p>
  </div>
</section>

<footer>
  <p>
    Pen by <a href="https://www.jemimaabu.com" target="_blank">Jemima Abu</a><span style="color: #D11E15"> &#9829;</span>
  </p>
</footer>
* {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 20px;
  padding-top: 54px;
  background-color: #fcfcfc;
  position: relative;
}

main {
  min-height: 100vh;
  max-width: 1240px;
  padding-bottom: 64px;
  margin: auto;
}

h1 {
  font-style: normal;
  font-weight: 800;
  font-size: 4.5em;
  line-height: 120%;
  letter-spacing: -0.02em;
  text-transform: uppercase;
  margin: 0;
}

h2 {
  margin: 0;
  font-weight: 600;
  font-size: 3em;
  line-height: 110%;
  display: flex;
  align-items: center;
  letter-spacing: -0.02em;
}

.caveat {
  font-size: 1.3em;
}

p {
  max-width: 721px;
  font-style: normal;
  font-weight: 400;
  font-size: 16px;
  line-height: 140%;
  margin: 0;
  margin-top: 35px;
}

.modal-btn {
  transition: background 250ms;
  padding: 16px 24px;
  border-radius: 4px;
  background-color: #3a3a3a;
  color: #fcfcfc;
  text-transform: uppercase;
  font-size: 12px;
  letter-spacing: 0.1em;
  margin-top: 32px;
  display: inline-block;
  text-decoration: none;
}

.modal-btn:hover,
.modal-btn:focus {
  background-color: black;
}

.modal {
  position: fixed;
  min-height: 100vh;
  width: 100%;
  top: 0;
  left: 0;
  display: flex;
  z-index: 2;
}

.modal:not(:target) {
  display: none;
}

.modal-overlay {
  width: 100%;
  height: 100%;
  position: absolute;
  background-color: rgba(0, 0, 0, 0.5);
  left: 0;
}

.modal-content {
  transition: transform 1s;
  background: #fff;
  width: 75%;
  position: relative;
  margin: auto;
  height: 75%;
  padding: 48px 24px;
  border-radius: 4px;
  max-width: 1000px;
}

.modal-close {
  font-size: 36px;
  text-decoration: none;
  color: inherit;
  position: absolute;
  right: 24px;
  top: 10px;
}

footer {
  position: absolute;
  width: 100%;
  left: 0;
  bottom: 0;
  text-align: center;
  padding: 16px;
  background-color: #eaeaea90;
  display: flex;
  justify-content: center;
}

footer p {
  color: #221133;
  margin: 0;
}

footer a {
  text-decoration: none;
  color: inherit;
}

/* Look ma, no JavaScript! */
const modal = document.getElementById('modal')

window.addEventListener('popstate', () => {
  const target = window.location.hash
  
  if (target === '#modal') {
    modal.focus();
    modal.setAttribute('aria-hidden', false);
    return
  }
  
  modal.setAttribute('aria-hidden', true)
});

window.addEventListener('keydown', (e) => {
  if (e.key == "Escape" && window.location.hash === '#modal') {
    window.location.hash = ""
  }
})

External CSS

  1. https://codepen.io/tutsplus/pen/vYrpEwd.css

External JavaScript

This Pen doesn't use any external JavaScript resources.