Redirecting a CSS file based on .htaccess rules

Question

I'm trying to hack the CSS files on OSTicket by replacing them with my own custom ones when a specific URL is accessed.

The URL that is accessed for this example is:
http://example.com/helpdesk/scp/css/main.css

and I would like it to use the CSS file at:
http://example.com/test.css

Why won't this .htaccess file (in web root, not /helpdesk/scp/) work? Is there an easy way to debug these rules, some way to find out what Apache did when the URL was accessed and where it's failing? error.log doesn't show anything useful.

RewriteEngine On

RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteRule ^(.*)main\.css$ /test.css [NC, L]

Answer 1

Delete space between NC, and L. Also check AllowOverride All (or FileInfo):

RewriteEngine On
RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteRule ^(.*)main\.css$ /test.css [NC,L]

Answer 2

See the documentation on RewriteLog and RewriteLogLevel for how to debug rewrite rules.