Yeah... see the comment on the LESS rule for it.  Essentially, to get the line centered in the gap between columns we need its offset to be some percentage plus half the fixed-size gap.  I suppose we could use `calc()` for that but I've always been a little unsure how well non-IE browsers support that stuff...

Fwiw the `.content-bottom` div is another thing we only need for layout, since it's impossible to put a margin/padding gap directly between floated content and an immediate sibling (e.g. see http://stackoverflow.com/questions/4198269/in-css-margin-top-is-not-working-with-clear-both).