This theme is based on the Ayu Mirage(ish) Color Scheme by @dempfi - Ayu. I merely just selected these colors and made an Atom UI theme because I could not find one.
Install the Ayu Mirage(ish) UI Theme via Atom by going to [Preferences/Settings > Install] and search for Ayu Mirage(ish) UI Theme (make sure you're searching under 'Themes'), or install through CLI
$ apm install ayu-mirage-ish-syntax
The Ui theme used in the screenshots is one-dark-ui