cocinado boton para volver arriba

src/lib/components/MostrarVolver.svelte.ts

@@ -0,0 +1,16 @@
+export class MostrarVolver {
+	scrollY = $state(0);
+	value = $derived(this.scrollY > 500);
+
+	constructor() {
+		if (typeof window !== 'undefined') {
+			$effect(() => {
+				const handleScroll = () => {
+					this.scrollY = window.scrollY;
+				};
+				window.addEventListener('scroll', handleScroll);
+				return () => window.removeEventListener('scroll', handleScroll);
+			});
+		}
+	}
+}