JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="card">
    <textarea rows="6" placeholder="Not highlighted"></textarea>
    <textarea rows="6" class="is-highlighted" placeholder="Highlighted"></textarea>
    <div class="overlay"></div>    
  </div>
</div>

CSS

.container {
  padding: 2rem;
  background-color: rgb(239, 96, 48);
}

@keyframes slide-down {
  0% {
    transform: translate(0, -1rem);
  }

  100% {
    transform: translate(0, 0);
  }
}

.card {
  padding: 1rem;
  background-color: white;
  animation: slide-down 0.8s normal forwards;
}

.is-highlighted {
  position:relative;
  z-index:2;
}

.overlay {
  position: fixed;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.4);
  z-index: 1;
  
  transition: 0.8s all;
}

JavaScript

let overlay = document.querySelector('.overlay');

// Ultimately, I want to make the overlay disappear after some time,
// but that's beyond the point.  

/*
window.setTimeout(() => {
  overlay.style.opacity = 0;
  window.setTimeout(() => {
    overlay.style.display = 'none';
  }, 800);
}, 800);
*/