What kind of error do you get? Have you verified the error and access log files of your web server? From these files you can check the generated error codes.
This is working for me:
RewriteRule ^(css|images|js|fonts) - [L]
RewriteRule ^([0-9]+)/([a-zA-Z0-9_-]+)$ index.php?id=$1&page=$2 [L]
If you try to access directly to the CSS file what header responses and contents do you get? If it is not configured properly, the server will try to return the index page contents instead of the CSS file. Usually the browser will return a blank page or will not reload. So you can try to debug by using: