chore: change back button variant to outline (#505)

Fixes #499 

<img width="1470" alt="Screenshot 2024-08-16 at 4 42 36 PM"
src="https://github.com/user-attachments/assets/6c122021-329c-4e1c-8ac8-50e2dd92060b">

frontend/src/components/layouts/TwoColumnFullScreenLayout.tsx

@@ -94,7 +94,7 @@ export default function TwoColumnFullScreenLayout() {
             // show the back button on setup pages, except the setup finish page
             <Button
               type="button"
-              variant="secondary"
+              variant="outline"
               onClick={() => {
                 navigate(-1);
               }}