This is what I have so far:
RewriteRule ^([A-Za-z0-9_]*)/?$ index.php?page=$1 [NC] RewriteRule ^([A-Za-z0-9_]*)/([A-Za-z0-9_]*)/?$ index.php?page=$1/$2 [NC]
... it assumes the css is located in /whatever/ssi/*.css. I just want to be able to write a condition that says "if it's a css file, don't apply these rules."
This translates directly to
RewriteCond %{REQUEST_URI} !^/whatever/ssi/[^/]+\.css$ RewriteRule ...