<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>