I can't find any references to this anywhere, in fact

This is on an element that clearly has no styles defined on itself:

So what does that mean? What is it referring to?

CodePudding user response：

To make the comment an answer:

It means there's a <style> element on the page with those rules, e.g.

<style>
.edit-action-dialog ... { ... }
</style>

You can use e.g. document.querySelectorAll("style") to enumerate those.