This app was mentioned in 3 comments, with an average of 1.33 upvotes
Outline theme https://play.google.com/store/apps/details?id=com.schnettler.outline Ethereal theme https://play.google.com/store/apps/details?id=com.schnettler.ethereal
Outline Substratum Theme
Outline
It's a Layers theme. Great theme with many colour options. Font that I'm using is Segoe UI.