JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <p>Some text</p>
</div>
<button>Add</button>

CSS

@keyframes flash {
  0% {
    opacity: 1;
  }
  
  50% {
    opacity: 0.3;
  }

  100% {
    opacity: 1;
  }
}

.flash {
  animation-name: flash;
  animation-duration: 500ms;
  animation-iteration-count: 2;
}

JavaScript

var div = document.querySelector('div')
var button = document.querySelector('button')

button.addEventListener('click', function () {
  var p = document.createElement('p')
  p.textContent = 'Some more text'
  p.className = 'flash'
  div.append(p)
})