I made the switch to VSCode, this theme is no longer under development. I'll leave this up for anyone to fork.
Nucleus is an adaptable UI theme for Atom with your favorite syntax coloring at its core! This gives the UI a coherent feel, with whatever syntax theme you like to use. I used Behave in the screenshot below.
Inside atom go to settings, select Install and search for Nucleus.
Or install directly from the console:
apm install nucleus-dark-ui
Every color used in the UI is taken directly from a (dark) syntax theme. In order for this to work, the syntax theme needs to have a syntax-variables.less. A light version of this theme is still being worked on.