Redesign guest pages for better accessibility

- Use white box and put content on it
- Improve focus indicator

Signed-off-by: Carl Schwan <carl@carlschwan.eu>

Author: CarlSchwan

core/Controller/LoginController.php

@@ -205,6 +205,7 @@ public function showLoginForm(string $user = null, string $redirect_url = null):
 		];
 
 		$this->initialStateService->provideInitialState('core', 'countAlternativeLogins', count($parameters['alt_login']));
+		$this->initialStateService->provideInitialState('core', 'alternativeLogins', $parameters['alt_login']);
 
 		return new TemplateResponse(
 			$this->appName,