One of the hottest trends right now is your app to have a dark background, and all app developers are not also lagging behind. Google has already released Dark theme for plenty of its applications, and now Gmail will get it too. It expected to be hitting users with Android 10 and iOS 11 or higher, but might take up to two weeks before it gets to all devices.
— Gmail (@gmail) September 24, 2019
All those using Google Pixel smartphone, will automatically have their Gmail app be in Dark theme once you have Battery Saver enabled. It will also respect the system default settings, if you decided to have all black everything.
How To Activate Dark Mode On Gmail App
However, if you want ONLY the Gmail app to be dark, simply go to Settings -> Theme -> Dark.
Apple users with iOS 11 or 12 should also look for the option in Settings, while for those who already are rocking the latest version, will receive it automatically if they’ve already set up total blackout for the UI. Once again – if you want only Gmail to be in Dark Mode, look for the toggle in Settings.
Dark Mode will be available both for regular customers and G Suite accounts once you update your application.