This is just edited original One Dark syntax, but this syntax is made more colorful and darker.
Try to compare the images when you open them in a new tab.
Original one dark syntax
Darker one dark syntax
I recommend to use this syntax with original one-dark UI theme, it looks way better than the other built-in UI themes.
Via command line
apm install darker-one-dark-syntax
Go to Settings > Install and next to the search bar select themes, than search for
darker-one-dark-syntax. And install it obviously.
After installing, go to Settings > Themes > Syntax Themes and select "darker-one-dark-syntax" from the drop-down menu.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.