Htaccess: changes root and doesn't find files - php

Question

I have a htaccess file that I am try to make a rewrite but it causes me multiple problems. First here is my htacess file:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^(.*)$ http://%1/ [R=301,L]
RewriteRule ^([a-zA-Z0-9]*)/?$ index.php?category=$1&%{QUERY_STRING}
RewriteRule ^([a-zA-Z0-9]*)/([a-zA-Z0-9]+)/?$ index.php?category=$1&itemId=$2&%{QUERY_STRING}
RewriteRule ^login$ login.php?category=$1&%{QUERY_STRING} [L]
The first problem is that when I make a request like "mysite/foo/bar/", it does rewrite the query string in category and itemId but it also changes the base directory for my css files and Js files to /foo/bar/design/css/style.css
The second problem is that I have a few path like "login/","register/","users/", and when I try to load the corresponding file, it says:
The requested URL /login/ was not found on this server.
Thanks for the help!

Answer 1

First change your .htaccess like this:
RewriteEngine On
## If the request is for a valid directory
RewriteCond %{REQUEST_FILENAME} -d [OR]
## If the request is for a valid file
RewriteCond %{REQUEST_FILENAME} -f [OR]
## don't do anything
RewriteRule ^ - [L]
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^(.*)$ http://%1/ [R=301,L]
RewriteRule ^([a-zA-Z0-9]*)/?$ index.php?category=$1 [L,QSA]
RewriteRule ^([a-zA-Z0-9]*)/([a-zA-Z0-9]+)/?$ index.php?category=$1&itemId=$2 [L,QSA]
RewriteRule ^login/?$ login.php?category=$1&%{QUERY_STRING} [L,QSA]