[jameshart]

Yes! This example is a control that toggles the visibility of part of the page. It is neither a link nor a button

And, you know, if you think about this from an assistive technology point of view, does a screenreader user actually need to worry about interacting with a control to make something visible? Isn't it better from their point of view to skip the interaction entirely and just put the list of theme options semantically under a navigable page heading?

[tempestn]

In this specific example, is the visual theme of the page even relevant to a screenreader user at all?

[DitheringIdiot]

A lot of screen reader users are partially blind, in the process of losing their site, or sharing a screen with someone else. So it’s better to give both experiences at the same time