css not working after writing .htaccess

I was trying to get rid of my file extensions using .htaccess, it worked, but right now my CSS and images has stopped working. I have tried different things, but it's still not working. Please! I need help with this. Thanks in advance. All my php files are in the same directory which is the root folder and my css and image folder is in a different folder in my root folder. here is my code

RewriteEngine On
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule !.*/.php$ %{REQUEST_FILENAME}.php [L]
RewriteRule ^(css|img) - [L]