It is not a native HTML page.
What ClassicPress and WordPress for what matters too do is have a PHP structure that allows a site owner to install a theme and plugins.
The theme is what takes care of front-end appearance (what you see as an HTML page) and is composed by PHP files, JS files and CSS files. Some of those files are what we call templates, they tell ClassicPress core the HTML markup and structure the site must use to render content. There is a template to show a list of articles for example (a blog page or the homepage if you set it to show latest posts), with a specific PHP function in it called loop. The loop does two things: asks the PHP to extract from the database the list of posts and is contained inside HTML markup so that when the template is used the page shows according to that markup the list PHP returned. ClassicPress core knows what each template is for (this is identified by specific names and file headers that are standard).
A person visiting the site and inspecting the page with developer tools sees the rendering of the template that the specific page they are inspecting uses - in the form of HTML markup and CSS styles. The page is generated by means of PHP and renders a result in styled HTML markup on front-end.
Now to the fun part: to “build the page” you have basically two ways.
Both start by going to Page>Add New, then you can:
- write the content and format it using the editor (you can enhance the editor by installing FX Builder and related plugins
so that you have more design options, shortcodes and all the whistles and bells of a page builder without the hassle of a page builder) - this is done in the visual part of the editor
- write HTML code in the text part of the editor (for this you can use the natural theme CSS to style your HTML so that you have it consistent with all the rest of the site and you do not have to write CSS or write your own CSS in the Customizer CSS section if your content needs some more CSS that is not included in the theme own CSS)
Once you have the content in place you save it. ClassicPress will use one of the templates supplied by the theme for that content. On the front-end inspecting the page will show HTML markup - but it’s a PHP template rendered correctly.
ClassicPress main website is a website built with ClassicPress. The home page of that site is simply a ClassicPress website page. I do not know who made it specifically but I think the method used was writing the content as HTML markup in the text tab in the ClassicEditor in ClassicPress when editing the page.
Without going too far, something similar can be achieved using the aforementioned FX Builder suite of plugins and a good barebones theme and your specific CSS or a good theme with a CSS that appeases your aesthetic sense.
Small Note: every website (no matter the stack used to build it, be it WP, CP, Joomla, Laravel, etc) will always render only HTML markup and styles on the front-end. because the back-end stack is used to make it work - not to show the content.
ClassicPress is a PHP based CMS, PHP powers all its functions, themes are a specific extension within the CMS used to take care of content rendering in HTML markup. Joomla is another PHP based CMS with “Layouts” taking care of rendering. If you inspect both types of sites (a Joomla and a CP one) what you will see is HTML and CSS and nothing else. And both have PHP under it to make them work correctly.
If a site shows up something else you need to close the tab real quick because there is something fishy… 