With the iPhone X using an OLED display, some app developers are catering to the display's strengths, offering dark modes that will help the smartphone save power. Unlike a traditional LCD panel that illuminates the whole screen regardless of what is being displayed, an OLED display is a bit more efficient, capable of illuminating individual pixels.
The Wikipedia app for iOS was recently updated to take advantage of the iPhone X's OLED display, as it introduced a new black theme, that should reduce battery consumption on the smartphone. In order to enable this, you'll have to head to the app's settings page, and under the appearance option, select the black theme. Along with the theme, the new version of the app also offers faster load times on articles and uses less data. It does this by having images download only when they are about to be displayed or when they are saved.
The app description also mentions the addition of an 'expand tables' option that will open information tables by default when enabled in the Appearance settings menu. Lastly, the app has also been improved with a lot of small bug fixes. Those interested can head to the App Store to download version 5.7.3 of Wikipedia.