在表单中创建弹出窗口

<button id="popupButton">点击打开弹出窗口</button>

<div id="popupWindow" class="popup">
  <div class="popup-content">
    <span class="close">&times;</span>
    <h2>弹出窗口标题</h2>
    <p>弹出窗口内容</p>
  </div>
</div>

.popup {
  display: none;
  position: fixed;
  z-index: 9999;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  overflow: auto;
  background-color: rgba(0, 0, 0, 0.5);
}

.popup-content {
  background-color: #fefefe;
  margin: 15% auto;
  padding: 20px;
  border: 1px solid #888;
  width: 80%;
}

.close {
  color: #aaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: black;
  text-decoration: none;
  cursor: pointer;
}

var popupButton = document.getElementById("popupButton");
var popupWindow = document.getElementById("popupWindow");
var closeButton = document.getElementsByClassName("close")[0];

popupButton.onclick = function() {
  popupWindow.style.display = "block";
}

closeButton.onclick = function() {
  popupWindow.style.display = "none";
}

window.onclick = function(event) {
  if (event.target == popupWindow) {
    popupWindow.style.display = "none";
  }
}