pathing to assets not working using rewrite

[Matthew Smith <chedderslam@xxxxxxxxx>]

I am trying to serve a secondary site from a subdirectory on my local server.

Here is my htaccess:

RewriteCond %{HTTP_HOST} mysitedotcom [NC]

RewriteCond %{REQUEST_URI} !^/site_mysite_com/ [NC]

RewriteRule (.*) /site_mysite_com/$1 [L]

RewriteCond %{REQUEST_URI} ^/site_mysite_com/ [NC]

RewriteCond %{HTTP_HOST} !mysitedotcom [NC]

RewriteRule . http://%{HTTP_HOST}/ [R=301,L]

The page is coming up, but assets like the css and images are not working when they were before(this is a fresh install of apache).

so I cannot get this to load in the html:

/css/style.css

but this works:

/site_mysite_com/css/style.css

Any ideas what I am doing wrong?  I thought the point of the rewrite was to redirect requests to the proper subdirectory.  I'm not sure if my htaccess is correct; I used my host's generator for it.  It is working on the live site.

Thank you.