The font used in this screenshot is Fira Code
I really liked the theme that is used for the screencasts on the atom ide promotional page. I hear that the developer that did the screencasts is out of office for some months and that the theme he/she was using was a custom theme that hasn't been released. So I made it! I based this off of Atom One Dark Syntax.
I haven't tested this for many languages, so if you see any odd syntax highlighting for a language, please submit an issue.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.