如何在所有其他对话框中显示对话框？

<div id="myModal" class="modal">
  <div class="modal-content">
    <span class="close">&times;</span>
    <p>这里是对话框的内容。</p>
  </div>
</div>

.modal {
  display: none;
  position: fixed;
  z-index: 999;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  overflow: auto;
  background-color: rgba(0, 0, 0, 0.4);
}

.modal-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;
}

// 获取对话框元素和关闭按钮元素
var modal = document.getElementById('myModal');
var closeBtn = document.getElementsByClassName('close')[0];

// 点击关闭按钮或对话框外部时，关闭对话框
closeBtn.addEventListener('click', function() {
  modal.style.display = 'none';
});

window.addEventListener('click', function(event) {
  if (event.target == modal) {
    modal.style.display = 'none';
  }
});

// 打开对话框
function openModal() {
  modal.style.display = 'block';
}