The standard style of Jira (Core) shows {code} ... {code} segment with a grey background but inline comments have a transparent background.
Example:

I would like to format the background of the inline-comment so that it is also grey.
This is what i want:

Where can i do that in Jira Core/Software? Maybe you can even tell me how to format more than that. I have little knowledge in CSS and html so i should be fine after a hint to the location.
Is it possible to edit Confluence to do the same formatting (say red background)