Add CSS without overriding theme

[rap2hpoutre]

Maybe I misunderstood something but it seems the CSS theme must be fully replaced if I want to add a rule. So if I did understand well, if I just want to add a simple rule (ex: h1 { color: #f00; }) I must copy the original file then add my rule at the end of the file.

If so, maybe we should add the possibility to create an optional custom.css where we could add our simple rules over the existing ones? I could submit a PR if you want.

[steveklabnik]

You are right, but this is almost an exact duplicate of https://github.com/azerupi/mdBook/issues/178, down to the file name! 😄 So thanks, but closing as a duplicate.

[rap2hpoutre]

Oops.