JSFiddle - React, Tailwind, and code Playground

HTML

<!-- Menu jest schowane -->
<nav>

<input type="button" value="Zamknij menu" onclick="showMenu();">
<input type="button" value="Otworz menu" onclick="hideMenu();">
  <ul id="main-menu">
    [...]
  </ul>
  
  
<script>
  function showMenu() {
  document.getElementById('main-menu').style.visibility='hidden';
}
 
function hideMenu() {
  document.getElementById('main-menu').style.visibility='visible';
}

</script>
</nav>

CSS

#main-menu{
  visibility:hidden;
}