Asciidoc toc always rendered at top?

I’m laying out a project README.adoc file, and I’d like to include a left side navigation element (similar to how the GitLab help pages work, although those are on the right). I’ve added

:toc: left

to the top of the document. This renders a left side navbar when I use asciidoc to create HTML from the page, and also renders properly in my IDE (GoLand, in this case). But, it looks like GitLab always renders the README.adoc file with the TOC element at the top of the page, as if it were just

:toc:

This happens when visiting the project root (where README.adoc resides), or when viewing the README.adoc file itself (by clicking on it in the project root).

Is there a way to get GitLab to render the TOC on the side, instead?

Well, let me answer my own question, having actually read AsciiDoctor’s doc on TOC placement all the way to the bottom… embeddable HTML always has the TOC rendered at the top.

If there happens to be some other way to do the same thing, though, I’d love to know!

Are using the AsciiDoctor tool chain? You might want to take a look at Antora which has more control over the navigation UI.