Не могу понять как реализовать всплывание маленького окна с покупками

document.getElementById("cartIcon").addEventListener("click", function() {
  var dropdown = document.getElementById("cartDropdown");
  if (dropdown.style.display === "none") {
    dropdown.style.display = "block";
  } else {
    dropdown.style.display = "none";
  }
});

window.onclick = function(event) {
  if (!event.target.matches(".cart-icon")) {
    var dropdown = document.getElementById("cartDropdown");
    if (dropdown.style.display === "none") {
      dropdown.style.display = "block";
    }
  }
};

.shop {
  margin-top: -1rem;
  margin-left: 20rem;
  position: absolute;
  transition: all 0.3s;
  width: 2rem;
  filter: invert(100%) sepia(0%) saturate(000%) hue-rotate(1deg) brightness(99%) contrast(70%);
}

.shop:hover {
  width: 2.5rem;
  filter: invert(20%) sepia(20%) saturate(10000%) hue-rotate(1deg) brightness(100%) contrast(50%);
}

<div class="conteiner-shop">
  <img class="shop" src="img/shop.png" alt="img">
</div>