I haven't used any CSS for those, it's just how it looks on the native layout. But adding this:

.metadata.bottom-metadata {
border-top: 0px solid #ffffff;
}

removed the line above the metadata. However, this:

.entry-poster {
border-top: 0px solid #ffffff;
}

didn't do anything and the line is still under the title Nevermind, figured this one out, it was border-bottom, not border-top!

I'm not trying to move my whole page down, I just want to create some space under the navigation strip (edit: I mean the navigation links which on my layout is a strip under the header. Apologies for the bad wording!). Increasing the margin-top value in #canvas moves the entire body further down.