This Atom theme is identical to the original One Dark theme, except that the colors are more vivid.
The font used in the screenshot is Fira Mono.
apm install one-dark-vivid-syntax
Or go to Settings > Install and search for
Then after installing, select "One Dark Vivid" from the Settings > Themes > Syntax Themes drop-down menu.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.