svelte/site/content/tutorial/10-transitions/04-custom-css-transitions/app-a/App.svelte

<script>
	import { fade } from 'svelte/transition';

	let visible = true;

	function spin(node, { duration }) {
		return {
			duration,
			css: t => ``
		};
	}
</script>

<style>
	.centered {
		position: absolute;
		left: 50%;
		top: 50%;
		transform: translate(-50%,-50%);
	}

	span {
		position: absolute;
		transform: translate(-50%,-50%);
		font-size: 4em;
	}
</style>

<label>
	<input type="checkbox" bind:checked={visible}>
	visible
</label>

{#if visible}
	<div class="centered" in:spin="{{duration: 8000}}" out:fade>
		<span>transitions!</span>
	</div>
{/if}