adopt-styles/index.html

<script type="module">
	import AdoptStyles from "/AdoptStyles.js"
	customElements.define("adopt-styles", AdoptStyles)
</script>

<style>
	.inline { color: red }
	@layer foo {
		.layer { color: purple }
	}
</style>

<link rel="stylesheet" href="/linked.css">

<my-component>
	<template shadowrootmode="open">
		<adopt-styles adopt="all"></adopt-styles>
		<p class="inline">Inline</p>
		<p class="layer">Layer</p>
		<p class="linked">Linked</p>
	</template>
</my-component>