One UI provides default themes and a dark mode. It’s recommended that you provide a dark mode so that the user can use their smartphone comfortably, even in a dark environment.
Using the default themes, you can apply a different color to the background according to the app’s characteristics. A lighter background can deliver a more comfortable visual experience because it reduces the contrast of the screen in general. It also helps improve the legibility of on-screen text.
A darker background can make a content item or dialog inside a focus block visually stand out more.
In particular, if you use a black background on the screen when the device’s bezel is also black, the boundary between the bezel and screen becomes merged, making the screen appear more visually expanded. This also reduces visual interference that the boundary between the bezel and screen may create.
Dark mode is a theme (mode) that enables the screen to turn darker to help reduce glare and eye strain at night or in a dark environment. Place dark colored focus blocks, dialogs, content and control components to keep the entire screen darker.
One UI recommends that all apps allow the user to switch to Dark mode at the desired or set time.