JSFiddle - React, Tailwind, and code Playground

HTML

<div class="some-class">Ein Element</div>

CSS

@keyframes fade-in {
  from {
    opacity:0;
  }
  to {
    opacity:1;
  }
}

body.animate .some-class {
  animation: fade-in 5s;
}

JavaScript

if(!window.localStorage.getItem('recurring_user')) {
	document.querySelector('body').classList.add('animate');
}
  
window.localStorage.setItem('recurring_user', 1);