site: fix immutable tutorial and example on Firefox (#2601)

site/content/examples/20-miscellaneous/02-immutable-data/flash.js

@@ -1,4 +1,5 @@
 export default function flash(element) {
+	requestAnimationFrame(() => {
 		element.style.transition = 'none';
 		element.style.color = 'rgba(255,62,0,1)';
 		element.style.backgroundColor = 'rgba(255,62,0,0.2)';
@@ -8,4 +9,5 @@ export default function flash(element) {
 			element.style.color = '';
 			element.style.backgroundColor = '';
 		});
+	});
 }

site/content/tutorial/16-special-elements/07-svelte-options/app-a/flash.js

@@ -1,4 +1,5 @@
 export default function flash(element) {
+	requestAnimationFrame(() => {
 		element.style.transition = 'none';
 		element.style.color = 'rgba(255,62,0,1)';
 		element.style.backgroundColor = 'rgba(255,62,0,0.2)';
@@ -8,4 +9,5 @@ export default function flash(element) {
 			element.style.color = '';
 			element.style.backgroundColor = '';
 		});
+	});
 }

site/content/tutorial/16-special-elements/07-svelte-options/app-b/flash.js

@@ -1,4 +1,5 @@
 export default function flash(element) {
+	requestAnimationFrame(() => {
 		element.style.transition = 'none';
 		element.style.color = 'rgba(255,62,0,1)';
 		element.style.backgroundColor = 'rgba(255,62,0,0.2)';
@@ -8,4 +9,5 @@ export default function flash(element) {
 			element.style.color = '';
 			element.style.backgroundColor = '';
 		});
+	});
 }