The technology behind a website is pretty much irrelevant to your SEO, as long as it can:
- fast load
- Have the content in the correct HTML tags (title, H1, H2, etc)
- Have well-defined meta tags
- Have friendly URLs
- be responsive
- Use HTTPS(etc)
The point is, you can do it all with any website building technology.
What you can do with just HTML and CSS is ridiculously limited compared to a complete system built in PHP (remembering that WordPress pages are rendered in HTML, CSS and JS anyway).
So you just want a static page? HTML + CSS! See this page: The Best Motherfucking Website Yes, it’s satire, but it’s all true. From a technical point of view it is a very well done page. But it doesn’t do much, do you agree?
If your purpose is to have a content system (like a blog), then my recommendation will always be WordPress, as it is super optimized for SEO (with the right theme), while meeting the basic needs to have a useful website.
Ah, but never forget: your question is extremely irrelevant if the content on your page (static HTML, PHP, Rails, etc) is not of good quality 😉