Laravel - If has errors on validation, insert class in the specifics inputs

I'm totally noob in PHP, but my question is, after the validation which has errors for specific inputs, how can I insert a class in the specific input?

Example, if i have this error in the validation: "The email field is required."

How can i insert a specific class in the email input?

Login routes:

Route::group(['prefix' => 'admin'], function () {
    Route::get('/', 'Admin\AdminController@index');

    Route::get('login', 'Admin\AuthController@getLogin');
    Route::post('login', 'Admin\AuthController@postLogin');
    Route::get('logout', 'Admin\AuthController@getLogout');
});

AdminController:

class AdminController extends AdminBaseController
{

    public function index()
    {
        if(Auth::user()){
            return view('admin/pages/admin/index');
        }

        return view('admin/pages/login/index');
    }

}

AuthController:

class AuthController extends Controller
{

    use AuthenticatesAndRegistersUsers, ThrottlesLogins;

    private $redirectTo = '/admin';

    public $loginPath = '/admin';

    public function __construct()
    {
        $this->middleware('guest', ['except' => 'getLogout']);
    }

    public function getLogin()
    {
        if(Auth::user()){
            return redirect('/admin');
        }

        return view('admin/pages/login/index');
    }

    public function postLogin(Request $request)
    {
        $this->validate($request, [
            'email' => 'required|email',
            'password' => 'required|min:6',
        ]);
    }
}

My blade form:

<form class="s-form" role="form" method="POST" action="/admin/login">
    <input type="hidden" name="_token" value="{{ csrf_token() }}">
    <div class="s-form-item text">
        <input type="text" name="email" value="{{ old('email') }}" placeholder="Email">
    </div>
    <div class="s-form-item text">
        <input type="password" name="password" value="{{ old('password') }}" placeholder="Senha">
    </div>
    <div class="s-form-item">
        @if ($errors->has())
            <div class="alert alert-danger">
                @foreach ($errors->all() as $error)
                    {{ $error }}<br>
                @endforeach
            </div>
        @endif
    </div>
    <div class="s-form-item s-btn-group s-btns-right">
        <input class="s-btn" type="submit" value="Entrar">
    </div>
</form>

via Chebli Mohamed