<div class="item"></div>
<div class="item"></div>
<div class="item"></div>

body {
  display: grid;
  grid-template-columns: repeat(3, 1fr );
}

.item {
  width: 200px;
  height: 100px;
  background-color: gray;
}

.item.active {
  background-color: red;
}

let items = document.querySelectorAll('.item');

items.forEach(function(item) {
  item.addEventListener("click", () =>{
    item.classList.add('active');
});
});