mod rewrite unknown folder location

Hi,

I'm working on a php software that will have the default css in the following location:

templates/default/css/main.css

I am using the following mod_rewrite:

RewriteRule ^css/main.css$ template/default/css/main.css [L]

Code (markup):

But if the user adds new themes then default css location would change because of the folder name, I need to do the equivalent of the following but can't figure out how it should actually be coded?

Here are two examples I've tried that aern't working

RewriteRule ^css/main.css$ template/([a-zA-Z0-9-_]+)/css/main.css [L]

RewriteRule ^css/main.css$ template/$1/css/main.css [L]

Code (markup):