Make sure that all resources are loaded via HTTPS

[kosek]

Some pages are referencing CSS stylesheets over http:// only links. This prevents loading such resources in recent browsers, for example this page: https://docbook.org/docs/howto/howto.html

Common trick is to use URLs like //docbook.org instead of https://docbook.org. Browser then will use the same protocol as page was loaded over.

[ndw]

I think howto.html is committed as a source document. It's not generated by the site build.
You genereated it last time, didn't you?

[kosek]

Hmmm, my memory is aging, it has been 9 years since the last build ;-)
You are right sources and stylesheets for howto are in https://github.com/docbook/docbook/tree/master/relaxng/schemas/howto
I will see if I can still run the build and modify links.
However there could be other pages on the docbook.org with the same problem.

[ndw]

Let me see if I can merge that stuff into the site build.
There might be other places, but only if there are other pages that are built independently. I'll see if I can check for those.