pinafore/routes/_components/LoadingPage.html

<div class="loading-page {{shown ? '' : 'hidden'}}">
  <LoadingSpinner />
</div>
<style>
  .loading-page {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 150px;
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 50;
    transition: opacity 0.25s linear;
  }
</style>
<script>
  import LoadingSpinner from './LoadingSpinner.html'
  export default {
    oncreate() {
      setTimeout(() => {
        this.set({shown: true})
      }, 200)
    },
    components: {
      LoadingSpinner
    }
  }
</script>