I'd say it would depend on how the browser loads the css (?)

AFAIK, CSS is processed linearly, so if an entry appears twice, the last one will overwrite the previous ones. Since here the link for the external css is above the onsite markup, I would assume that the onsite markup should overwrite any of the external settings.

Of course, this is all just guessing, so don't quote me on that.

you can test this by setting certain values in both an external file and the onsite css and see who's got final word.