The agnostic-astro package utilizes XElement under-the-hood in order to provide build-time Astro components. These build-time components will help your project get closer to realizing a mostly no client-side runtime…if you do it right, this should mean an all-green 100% Lighthouse performance score! Leverage the benefits of Islands architecture by sending mostly server built agnostic-astro components. Then, sprinkle client-hydrated ones only as needed.

Ensure you've installed and setup the AgnosticUI Astro integration which will import the required common.min.css onto your page:

npm i astro-agnosticui

Then add the integration to your astro.config.mjs (you may need to run Astro with experimental integrations flag astro dev --experimental-integrations):

import { defineConfig } from 'astro/config';
import agnosticAstro from 'astro-agnosticui';;
export default defineConfig({
  integrations: [agnosticAstro()]
});

Then you can import Astro Spinner component (agnostic-astro ships with the astro-agnosticui integration):

import AgSpinner from 'agnostic-astro/Spinner.astro';

Here's the agnostic-astro Spinner component in use:

...
<AgSpinner showOnMount size="small" />
<AgSpinner showOnMount />
<AgSpinner showOnMount size="large" />
<AgSpinner showOnMount size="xlarge" />
<div class="mbs24 text-center">In 5 seconds a customized spinner will be shown below…</span>
<AgSpinner class="manuallyShow mbs40" showOnMount={false} size="xlarge" style="--agnostic-spinner-color: salmon;" />
...and so on
<script>
  setTimeout(() => {
    // aria-busy toggles spinner's visibility. By default showOnMount is true but
    // in this case, we've set: showOnMount={false} allowing control via JavaScript
    document.querySelector('.manuallyShow').setAttribute('aria-busy', 'true');
  }, 5000);
</script>