How to require a REFERER for a specific path in apache2 webserver?

Question

<Location /my-app/files>
    Require all granted
</location>

I want to restrict access to /my-app/files by using the %{HTTP_REFERER}. Let's for example I want to grant access only for linking by www.google.de and www.stackoverflow.com.

How could I combine my Location with a RewriteCond %{HTTP_REFERER}?