It’s not immediately clear to me why you’d want to do that, but the <body>
tag in topic pages has a unique class that’s added to it. That class is archetype-regular
You can use that to scope your style changes with something like this
.archetype-regular {
#main-outlet {
// styles go here
}
}
Personal message pages also have something similar and the class in that case is
archetype-private_message
If you want the changes to apply to PM pages, you can include them by adding the selector the the CSS above like so
.archetype-regular,
.archetype-private_message {
#main-outlet {
// styles go here
}
}
Fair warning though, changes to the #main-outlet
margins can have unintended consequences. More on that here.