This atom theme is a modification of One Dark Vivid that makes it even darker. It's meant to be used in conjunction with the one-dark-ui theme.
apm install kolsvart-syntax
Or go to Settings > Install and search for
Then after installing, select "Kolsvart" 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.