MacOS Mojave introduced a new system-wide dark mode. To turn it on, go to the Apple Menu - System Preferences - General. Now select Dark and the entire user interface will turn dark. To turn it off, select Light.
While in Dark mode, the dock, menu bar, and all of your Apple apps, including Safari, Mail, Calendar, Notes, the Mac App Store, Messages, and more will feature darker colors and themes.
Additionally, you have the option to select new accent colors. Choose the ones you desire to further tailor the looks of your macOS.
Do you like Dark Mode?