JSFiddle - React, Tailwind, and code Playground

HTML

<h1>Pierwszy</h1>
<div>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Maxime aperiam eum perspiciatis quo optio vero quas nostrum nam quae fuga.</div>
<h1>Drugi</h1>
<div>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Maxime aperiam eum perspiciatis quo optio vero quas nostrum nam quae fuga.</div>
<h1>Trzeci</h1>
<div>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Maxime aperiam eum perspiciatis quo optio vero quas nostrum nam quae fuga.</div>

CSS

h1 {
  cursor:pointer;
}
.ukryty {
  display: none;
}

JavaScript

var naglowki = document.getElementsByTagName("h1");

for(var i = 0; i <= naglowki.length; i++){
  
  naglowki[i].nextElementSibling.className = "ukryty";
  
  naglowki[i].addEventListener("click", function(){

    if(this.nextElementSibling.className == ""){
      this.nextElementSibling.className = "ukryty";
    } else {
      this.nextElementSibling.removeAttribute("class");
    }

  });

}