@Jim M
I have been using https for many years now, there are no problems with other addresses and mod_rewrite.
The config contains
'base_url' => 'https://mysite.com/',
The only problem with changing the theme, perhaps it was before, but I did not know about it, because I used a standard template.
I noticed that there is no "theme" folder in the installation archive, is this how it should be?
Here's my theme folder looks like
it doesn't have a file index.php, maybe that's the problem?