I have the following Short-hand for a user profile url
RewriteRule ^(\\w+)/?$ ./profile.php?name_of_user=$1
The site is styled with the app
the easiest way to fix this is to specify the full path to your CSS file in the of the HTML file.
If your mod_rewrite rule is modifying the path to where your CSS file is, you'd also want to place this before your RewriteRule:
RewriteCond %{REQUEST_FILENAME} !-f
This makes sure that the request doesn't match a file before rewriting it.