JSFiddle - React, Tailwind, and code Playground

HTML

<button type="button" onclick="Mudarestado('formulario');">
  Abrir div
</button>
<form id="formulario" action=" ">
  <input type="text ">
  <input type="text ">
</form>

CSS

#formulario {
  opacity: 0;
  transition: opacity 1.5s;
}

#formulario.mostrar {
  opacity: 1;
}

JavaScript

function Mudarestado(el) {
  document.getElementById(el).classList.toggle('mostrar');
}