htaccess RewriteBase

Question

I have two directories in my root: /dev and /live.

All content inside these directories have relative paths such as /css/style.css

Answer 1

RewriteBase lets you fix issues with how URLs get translated to file paths and back again. It's not for what you're using it for. Use a standard RewriteRule

RewriteCond %{REQUEST_URI} !^/live
RewriteRule ^(/?)(.*) /live/$2