Hovering over certain tags moves the robot up when the browser is narrow:
(At the width I'm at, it's only the second, third, and fourth tags on questions that trigger this on the Home pages, and the third, fourth, and fifth on the Questions page. However, other widths have other ranges of tags affected.)
What's happening is that it's creating a horizontal scrollbar, which pushes up some of the content, such as the robot and (if it's there) the cookie notice.
The scrollbar shows up on all sites, but it's most noticeable here because of the robot moving.
There's no reason to even create a scrollbar here because the content doesn't extend past the edge of the page.
The browser I'm using is Chrome on Mac.
Oh and there's also no reason to give new users nothing but enormous black boxes when they first get here. It sucks, although this is a completely different issue (I suggest everyone support the question here).