title: Change between Light and Dark mode for entire app
body: <p>I want to have a dark mode option within the settings page of my Xcode swift app. Is it possible to change dark mode just for the app, on all view controllers in the app? I have my dark colors selected in <code>Assets.xcassets</code></p>
  <p>I understand that I can use <code>overrideUserInterfaceStyle = .dark</code> but this only changes the one viewController. I want it to switch the entire app.</p>