Dark mode on your Mac is a little trick that users play to spice up their user-experience on screen. Once any user enables dark mode on his Mac OS X, s/he can view completely different screen, where the dock and menu bar background turns dark and fonts become white.
This gives them higher contrast menu bar and dock; this darkness creates a different experience to some users, who always want to do something unusual or weird. It is quite easy to enable dark mode on your Mac OS X; this will have some effect on Dock, menu bar, menu bar items and dropdown menu.
How to Enable Dark Mode on Mac OS X Yosemite and El Capitan
Step #1. Click on Apple menu → Launch System Preferences.
Step #2. Click on General.
On this page, you will find a check box: Use dark menu bar and Dock.
Step #3. Click in the check box.
This will show an immediate effect in the menu bar at the top of screen.
You can see additional dark mode theming if you click on menu bar items. Also check transparent dark background at the Dock; you don’t see that transparent light gray background any more.
If you are not happy with this dark mode or if your eyes are stressed out, you can disable the dark mode on your Mac OS X. All you need to do is to follow the same procedure as you did to enable dark mode; just click that check box again and the dark mode is disabled.
You can check the default settings, which are visible in the menu bar. The Dock on your Mac also appears in the brighter mode.
Watch out how to enable dark mode in Mac OS X El Capitan:
The dark mode feature is available only on OS X 10.10 and later.