Laravel 5 not find http://localhost:8000/css/app.css

I am using Laravel 5 and got "Failed to load resource, the server responded with a status of 404(Not Found) http://localhost:8000/css/app.css"

If my layout.blade.php were

   <link rel="stylesheet" href="http://ift.tt/1K1B2rp">

It works fine.

But If I changed it to

 <link rel="stylesheet" href="{{ URL::asset('css/app.css') }}">

I got

http://localhost:8000/css/app.css Failed to load resource: the server responded with a status of 404 (Not Found)

I have public/css/app.css which I got from gulp and it clearly exists these.

If I entered http://localhost:8000/css/app.css from browser URL, I got an error NotFoundHttpException in RouteCollection.php line 161:" because I do not write /css/app.css at routes.php.

But I do not think this is a routing issue.

I know very similiar issue in Stack Overflow but can not find specific solutions.

via Chebli Mohamed