The dark mode is coming to Gmail on mobile, and it will be available for download on Google pixel phones and other phones currently running on Android 10 or iOS 11 or higher. Not to worry, it's also coming to all devices, but that might be in about 15 days (2 weeks). To enable the dark theme on your gmail, simply go to settings >> theme >> select dark. If you're using a Google Pixel smartphone, Gmail will automatically switch to dark mode once you enable battery saver.