Make the version picker bigger and more obvious

The version picker is hidden down in the bottom left of the screen:

It is awesome that users can browse specific version of the docs, but it would be easy for a user to miss that they're looking at the docs for Olive vs Palm vs main.

Can we do anything to make that more conspicuous?

For historic context: The release process for the old documentation site involved changing the titles of book to indicate their version (e.g., Installing and Running: Juniper). That made the version obvious, but it's extra work for the release manager, so ideally on the new site we could just rely on the version picker.

The issue provides a screenshot of the current version picker but names no files, tests, or entry points. Start by locating the documentation site's version-picker UI, then determine how to make the selected documentation version conspicuous; done means users can readily distinguish Olive, Palm, and main without changing book titles.