The dark mode feature in the app changes background of the app to black. This also changes the various font/text colors accordingly in the entire app.
From the settings tab simply click the dark theme toggle button.
This will take the entire app from the current theme to the dark theme.
Below are the Snapshots for the Dark Mode theme of the app
Please note that the dark mode is independent of the system dark mode feature. If the system is set to dark mode the app can continue to be in a theme independent of the system. The app has its own theme setting which is a normal mode or the dark mode.