svelte/site/content/examples/modal-with-slot/App.html

<script>
	import Modal from './Modal.html';

	export let showModal;
</script>

{#if showModal}
	<Modal on:close="{() => showModal = false}">
		<h2 slot="header">
			modal
			<small><em>adjective</em>  mod·al \ˈmō-dəl\</small>
		</h2>

		<ol class="definition-list">
			<li>of or relating to modality in logic</li>
			<li>containing provisions as to the mode of procedure or the manner of taking effect —used of a contract or legacy</li>
			<li>of or relating to a musical mode</li>
			<li>of or relating to structure as opposed to substance</li>
			<li>of, relating to, or constituting a grammatical form or category characteristically indicating predication</li>
			<li>of or relating to a statistical mode</li>
		</ol>

		<a href="https://www.merriam-webster.com/dictionary/modal">merriam-webster.com</a>
	</Modal>
{:else}
	<button on:click="{() => showModal = true}">
		show modal
	</button>
{/if}