TOPIC:

after upgrading to 2.0 my site is only shown in some kind of graphic-free HTML. No Error-messages but the warning in the browser-address-field. (See attachment).

Your site is at https://

But the links to the CSS files are just http://

The browser is refusing to load them.

Look in the file data/config.ini.php

You should see a line base_url=...

Make certain this file has https:// and not http://

Thank you !
The missing "s" was the Problem. It works now.