How can I add a custom class to every 2nd message?

[Mittineague]

@ziptofaf

As the different color will spread way too much to the right and it looks poorly

That’s just basic CSS and a result of not targeting the correct element.

“small action” posts can be excluded from the styling easily enough by specifying the class value “topic-post”, but the odd-even uses the element regardless of the class attribute

div.post-stream > div.topic-post:nth-child(2n) div.topic-body {
  background-color: #bde;
}
div.post-stream > div.topic-post:nth-child(2n+1) div.topic-body {
  background-color: #edb;
}