Finding exact location with css, no javascript allowed

I'm doing progressive html rendering, part of the content relies on 3rd party APIS that the server is calling, however the content is at the very top of the page and it would just block rendering rest of the page.

What i would need is to execute API calling at the end and serve it as a last part of the html content.

So my question is, is there a way to create sort of "reference" point with just pure css to figure out where the content should be shown?

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