the-biergarten-app/web/frontend/app/root.tsx

import {
    isRouteErrorResponse,
    Links,
    Meta,
    Outlet,
    Scripts,
    ScrollRestoration,
} from 'react-router';

import type { Route } from './+types/root';
import './app.css';
import Navbar from './components/ui/navbar/Navbar';
import ToastProvider from './components/ui/toast/ToastProvider';
import { getOptionalAuth } from './features/auth/auth.server';
import { themeStorageKey } from './features/theme/themes';

const themeInitScript = `
  (function () {
    try {
      var theme = localStorage.getItem(${JSON.stringify(themeStorageKey)});
      if (theme) document.documentElement.setAttribute('data-theme', theme);
    } catch (e) {}
  })();
`;

export const links: Route.LinksFunction = () => [
    { rel: 'preconnect', href: 'https://fonts.googleapis.com' },
    {
        rel: 'preconnect',
        href: 'https://fonts.gstatic.com',
        crossOrigin: 'anonymous',
    },
    {
        rel: 'stylesheet',
        href: 'https://fonts.googleapis.com/css2?family=DM+Sans:ital,opsz,wght@0,9..40,100..900;1,9..40,100..900&family=Volkhov:ital,wght@0,400;0,700;1,400;1,700&display=swap',
    },
];

export const loader = async ({ request }: Route.LoaderArgs) => {
    const auth = await getOptionalAuth(request);
    return { auth };
};

export const Layout = ({ children }: { children: React.ReactNode }) => {
    return (
        <html lang="en">
            <head>
                <meta charSet="utf-8" />
                <meta name="viewport" content="width=device-width, initial-scale=1" />
                <Meta />
                <Links />
                <script dangerouslySetInnerHTML={{ __html: themeInitScript }} />
            </head>
            <body>
                {children}
                <ScrollRestoration />
                <Scripts />
            </body>
        </html>
    );
};

const App = ({ loaderData }: Route.ComponentProps) => {
    const { auth } = loaderData;
    return (
        <>
            <Navbar auth={auth} />
            <ToastProvider />
            <Outlet />
        </>
    );
};

export default App;

export const ErrorBoundary = ({ error }: Route.ErrorBoundaryProps) => {
    let message = 'Oops!';
    let details = 'An unexpected error occurred.';
    let stack: string | undefined;

    if (isRouteErrorResponse(error)) {
        message = error.status === 404 ? '404' : 'Error';
        details =
            error.status === 404
                ? 'The requested page could not be found.'
                : error.statusText || details;
    } else if (import.meta.env.DEV && error && error instanceof Error) {
        details = error.message;
        stack = error.stack;
    }

    return (
        <main className="pt-16 p-4 container mx-auto">
            <h1>{message}</h1>
            <p>{details}</p>
            {stack && (
                <pre className="w-full p-4 overflow-x-auto">
                    <code>{stack}</code>
                </pre>
            )}
        </main>
    );
};