How to style embedded comments?

We use the comments on our blog, and they work so well. (Including the custom Embedding CSS!)

I’d like to be able to style one particular topic/blog post’s comments slightly differently, but the only unique attribute I can find in the comment elements is each individual comment’s ID. Unfortunately these won’t do the trick, as I can’t maintain a CSS file for updating the styles for each new individual comment! I’ve also looked into using JavaScript to add the topic ID to list, but as none of the Customisable HTML gets embedded with the comments, no such luck.

Is there a unique attribute I’ve missed that I can use to hook CSS for one topic’s comments? Or any way that the topic ID can be added to the embedded HTML element in a future release? E.g.

<html data-topic-id="topic-1208">