[hhh]

<button class="gruppi-toggle">
Click
</button>
<div class="speciali-gruppi-window" style="display: block">Lorem ipsum dolor sit amet, consectetur adipisicing elit. Dolor ratione, pariatur obcaecati veritatis eum sit. Expedita quas suscipit esse aspernatur sint veritatis eius, dolores, architecto voluptate tempore illo itaque, eligendi.</div>

<script>
(function(){
  var btn = document.querySelector(".gruppi-toggle");
  var block = document.querySelector(".speciali-gruppi-window");
  
   if (window.screen.width < 960){
    btn.addEventListener("click", function() {
      if (block.style.display == "block") {
        block.style.display = "none";
      }
      else {
        block.style.display = "block";
      }
    });
   }
})();

</script>