17. Add extra elements/effects to make app look nicer

[Mama-simba]

Summary

We could also add some extra elements (icons), style buttons and give them some hover or focus effects to make the app look nicer.

Acceptance criteria

• Style buttons with shadows, hover, active or focus effects.
• Style error messages.
• Optional: add some icons from fontawesome or heroicons to the navigation menu and/or main header.
• Optional: add a Footer linking to contributors GitHub accounts.