mixed content: the page at '<url>' was loaded over https, but requested an insecure stylesheet '<url>'. this request has been blocked; the content must be served over https. code example

Example: mixed content: the page at '' was loaded over https, but requested an insecure stylesheet ''. this request has been blocked; the content must be served over https.

Here's your problem:

RewriteCond %{SERVER_PORT} ^443$
RewriteRule (.*) http://www.example.com/$1 
You don't allow SSL requests (443 port number is used for HTTPS requests). Try removing these lines.