How to Activate Dark Mode in OS X Yosemite

To activate dark mode in OS X Yosemite, follow these steps:

1. Click on the Apple menu in the top left corner of your screen and select System Preferences.

2. Click on General.

3. In the Appearance section, select "Dark" from the options.

4. Your screen will now switch to dark mode. You can switch back to the light mode by following the same steps and selecting "Light" from the options.

Alternatively, you can use the keyboard shortcut "Shift + Command + L" to toggle between dark and light mode.

Note that dark mode is only available on macOS Mojave or later, so if you're using an older version of macOS, you won't be able to access this feature.