Sapper

src/routes/_error.svelte

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+<script lang="ts">
+	export let status: number;
+	export let error: Error;
+
+	const dev = process.env.NODE_ENV === 'development';
+</script>
+
+<style>
+	h1, p {
+		margin: 0 auto;
+	}
+
+	h1 {
+		font-size: 2.8em;
+		font-weight: 700;
+		margin: 0 0 0.5em 0;
+	}
+
+	p {
+		margin: 1em auto;
+	}
+
+	@media (min-width: 480px) {
+		h1 {
+			font-size: 4em;
+		}
+	}
+</style>
+
+<svelte:head>
+	<title>{status}</title>
+</svelte:head>
+
+<h1>{status}</h1>
+
+<p>{error.message}</p>
+
+{#if dev && error.stack}
+	<pre>{error.stack}</pre>
+{/if}

src/routes/_layout.svelte

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+<script lang="ts">
+	export let segment: string;
+</script>
+
+<main>
+	<slot></slot>
+</main>