在Shopify admin内的嵌入式应用程序的页面之间添加加载指示器的最简单方法是什么？

<link rel="stylesheet" href="https://sdks.shopifycdn.com/polaris/5.10.0/polaris.min.css" />
<script src="https://sdks.shopifycdn.com/polaris/5.10.0/polaris.min.js"></script>

<div class="spinner-container">
  <div class="spinner"></div>
</div>

.spinner-container {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}

.spinner {
  border: 4px solid #f3f3f3;
  border-top: 4px solid #3498db;
  border-radius: 50%;
  width: 40px;
  height: 40px;
  animation: spin 2s linear infinite;
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}

document.addEventListener("DOMContentLoaded", function() {
  var spinnerContainer = document.querySelector(".spinner-container");
  spinnerContainer.style.display = "none";
});