How to get dark mode to work will depend on your phone on Android but  Google points out three ways to get it to turn on. They are:

In your Android Display system setting, set your device to dark theme—Gmail will automatically respect the system default setting. On Pixel, when Battery Saver is enabled, Gmail will default to dark theme automatically. Or, in Gmail go to Settings > Theme and select “Dark”.

On iOS things are slightly different with Google recommending the following:

For iOS 11 or 12, enable dark theme by going to Settings > Dark Theme. To enable dark theme on iOS 13, you can:Set your device to dark theme in iOS Settings, and Gmail, by default, will automatically respect the system default setting. Or, in Gmail go to Settings > Theme and select “Dark”.

Dark modes in general can be a little overhyped in their importance, but some people prefer the darker hues particularly at night. Also if you have a phone with an OLED display then it’ll save you battery life as it lights up fewer pixels then white-backed apps.

It continues Google’s slow rollout of dark mode across its apps and services – not every Google thing is dark right now and Gmail was one of the few remaining apps to get it.

Henry is Tech Advisor’s Phones Editor, ensuring he and the team covers and reviews every smartphone worth knowing about for readers and viewers all over the world. He spends a lot of time moving between different handsets and shouting at WhatsApp to support multiple devices at once.