如何在标记中显示弹出窗口？

<button id="popupButton">点击弹出窗口</button>

#popup {
  display: none;
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 300px;
  height: 200px;
  background-color: #fff;
  border: 1px solid #ccc;
  padding: 20px;
}

var popup = document.getElementById("popup");
var popupButton = document.getElementById("popupButton");

popupButton.addEventListener("click", function() {
  popup.style.display = "block";
});

popup.addEventListener("click", function(event) {
  if (event.target === popup) {
    popup.style.display = "none";
  }
});