There is a fundamental problem with the question, which is that HTML simply doesn't work that way, with very limited exceptions. Part of the current speed and power of the web is that HTML, CSS and Javascript are mostly separate files. In particular, CSS and Javascript are loaded separately, often from special servers (CDN = Content Delivery Network) so that files can be cached and/or many of the files loaded from someplace closer than the actual main web server. It is generally considered bad form to deliberately combine everything in one giant file, though it is technically possible to do so. As a result, most (if not all) modern page building software will, by design, create numerous separate files. The one exception is email. For historical and practical reasons, HTML email generally has to be a single file. Which means CSS embedded. In addition, many email systems (for very good reasons) will not process Javascript at all. But for regular sites - separate files.

Hello manassehkatz‭

I disagree with:

HTML doesn't work that way

There is a fundamental problem with the question

My case is one of the exceptions you talk about ...

Have you ever tried to develop in MediaWiki? If so you would know how easy such a tool would make layouting unique (non article) webpages there.

Edit: And if may I add, "for historical and practical reasons" :)