The Grammarly Keyboard for iOS and the Grammarly iPhone Editor automatically switch to dark mode if you have a dark theme activated on your iOS device. You only need to activate the dark mode in your iPhone's system settings, and the Grammarly Keyboard and iPhone Editor will adapt accordingly.
The Grammarly Keyboard for iOS also adapts to your device's app theme. If you have other apps set to dark mode, Grammarly will follow suit. Ensure that your device's app theme settings are configured to dark mode so Grammarly can appear in dark mode.