Forum users aren't allowed to advise help while editing parent themes.
Not quite true: There is no rule against making a suggestion to edit parent themes. All of us can and do offer advice on anything, it's just a good practice to recommend a solution to a problem that is sustainable.
Editing a theme directly can and has bitten people before when that theme has been updated and child themes are an insurance against that.
It's also one of my favorite WordPress features. ;)
However, some themes just can't work with a child theme and when that happens a plugin can get the CSS you need onto your site.
This is one that I've found to be easy and no-frills.
@slolavar, unless you can isolate the internal links vs external links with a specific CSS rule, that CSS will update all links.
Try using Firebug or a similar CSS tool to see if you can get more specific in your CSS.
Also you're using a commercial theme and support should have come with that purchase.
Try asking at http://graphpaperpress.com/support/ and see if they have a solution. We don't (can't really) support commercial themes here and our advice here would be pretty generic for you.