I've been trying to replicate this issue without any success. I've tried both Safari and Firefox and the current selector seems to be working fine. Is this specific to a particular browser version or configuration?

The problem with your change is that it will break the functionality of the code copy when the line numbers are enabled on the code block. If you remove .chroma from the selector, it will copy the line numbers instead of the actual code. There's an example of this type of code block on the Markdown Sample page in the exampleSite if you want to test to see what I mean.

I closed the PR but the problem still problem still exists, the exampleStie has same issue. I'm trying to figure out the root cause.

Finally, I found this issue is caused by bothnoClasses = true in [highlight]and enableCodeCopy = true.

Here are design options:

1. Show error message when both highlight.noClasses = true and .Site.Params.enableCodeCopy = true.
2. Enforce or overwrite highlight.noClasses = false when .Site.Params.enableCodeCopy = true.

Well highlight.noClasses = false is considered a theme requirement so I'm not sure this is actually a big problem to solve. Perhaps I could show a build warning if any of the required params aren't set though.

I've had a look into this and unfortunately Hugo doesn't allow themes to access the Markup config values and so I'm not able to add these warnings - see https://discourse.gohugo.io/t/how-do-i-get-the-noclasses-value/26395. I don't think there's much more I can add to this at this stage.

I've had a look into this and unfortunately Hugo doesn't allow themes to access the Markup config values and so I'm not able to add these warnings - see https://discourse.gohugo.io/t/how-do-i-get-the-noclasses-value/26395. I don't think there's much more I can add to this at this stage.

It looks the only thing we can do is to update configuration.md to highlight when enableCodeCopy = true that highlight.noClasses must be false.

I have made some changes to better explain these required params. Hopefully this makes it a bit clearer and will help others avoid this situation.