将自定义弹出窗口显示为完全不透明，如Page.DisplayAlert()

<div id="custom-popup">
  <p>This is a custom popup window.</p>
</div>

#custom-popup {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 200px;
  height: 200px;
  background-color: rgba(0, 0, 0, 1); /* 设置背景颜色为完全不透明的黑色 */
  color: #fff;
  text-align: center;
  padding: 20px;
}

function showCustomPopup() {
  var popup = document.getElementById("custom-popup");
  popup.style.display = "block";
}

function hideCustomPopup() {
  var popup = document.getElementById("custom-popup");
  popup.style.display = "none";
}