They don't have a common platform. They oppose each other's political ideas. As usual, Roscoe doesn't present the whole truth.
"As the Greens and Libertarians socialized after the forum, many were overheard expressing their willingness to support each other in races where both parties do not field candidates. Members of both parties feel the Democrats and Republicans are corrupt, and are pandering to big corporations while failing to protect the average American citizen’s constitutionally guaranteed rights."