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

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

@@ -1,11 +1,13 @@
 export default function flash(element) {
-	element.style.transition = 'none';
-	element.style.color = 'rgba(255,62,0,1)';
-	element.style.backgroundColor = 'rgba(255,62,0,0.2)';
+	requestAnimationFrame(() => {
+		element.style.transition = 'none';
+		element.style.color = 'rgba(255,62,0,1)';
+		element.style.backgroundColor = 'rgba(255,62,0,0.2)';
 
-	setTimeout(() => {
-		element.style.transition = 'color 1s, background 1s';
-		element.style.color = '';
-		element.style.backgroundColor = '';
+		setTimeout(() => {
+			element.style.transition = 'color 1s, background 1s';
+			element.style.color = '';
+			element.style.backgroundColor = '';
+		});
 	});
 }

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

@@ -1,11 +1,13 @@
 export default function flash(element) {
-	element.style.transition = 'none';
-	element.style.color = 'rgba(255,62,0,1)';
-	element.style.backgroundColor = 'rgba(255,62,0,0.2)';
+	requestAnimationFrame(() => {
+		element.style.transition = 'none';
+		element.style.color = 'rgba(255,62,0,1)';
+		element.style.backgroundColor = 'rgba(255,62,0,0.2)';
 
-	setTimeout(() => {
-		element.style.transition = 'color 1s, background 1s';
-		element.style.color = '';
-		element.style.backgroundColor = '';
+		setTimeout(() => {
+			element.style.transition = 'color 1s, background 1s';
+			element.style.color = '';
+			element.style.backgroundColor = '';
+		});
 	});
 }

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

@@ -1,11 +1,13 @@
 export default function flash(element) {
-	element.style.transition = 'none';
-	element.style.color = 'rgba(255,62,0,1)';
-	element.style.backgroundColor = 'rgba(255,62,0,0.2)';
+	requestAnimationFrame(() => {
+		element.style.transition = 'none';
+		element.style.color = 'rgba(255,62,0,1)';
+		element.style.backgroundColor = 'rgba(255,62,0,0.2)';
 
-	setTimeout(() => {
-		element.style.transition = 'color 1s, background 1s';
-		element.style.color = '';
-		element.style.backgroundColor = '';
+		setTimeout(() => {
+			element.style.transition = 'color 1s, background 1s';
+			element.style.color = '';
+			element.style.backgroundColor = '';
+		});
 	});
 }