Update 20/08/2019: I forgot to mention that this method only works on systems with a version of macOS up to 10.13. That's because macOS 10.14 Mojave includes a built-in out of the box dark mode. That was not known as of the writing of this post.

OS X is known to be light, extremely light. That's why, an user named @guilhermerambo created this tool, which makes any system control in any app dark and is easy as 1-2-3! But this tool is not the perfection. In fact it can only darken apps on a app per app basis, and once you quit an app, you lose the "dark mode". The developer even said:

The service I've written to enable dark mode in apps is just an experiment. You should not expect it to work or work reliably. I will not help anyone with this, it's just a proof of concept.

If an app contains few or none of the system's built-in controls, the tool will be useless.

Two more disclaimers by the developer:

Disclaimer 1: Please note that, while I have SIP disabled on my machine, I do not recommend it to anyone, it's an important security feature and you should only disable it if you know the implications.
Disclaimer 2: I am not responsible for any issues you might face while trying this out. If you computer blows up, it's not my fault.

So, with this on mind, let's start!

Requisites

Instructions

  1. Download this file and extract it to ~/Library/Services.
  2. Open the app you want to darken and press [NameoftheApp] > Services > Apply Dark Mode
  3. Wait ~10 secs and —voilà!—your app should be dark.