Google Calendar: The Theme option in the General section of the app’s settings.
Google Calculator: Hit the three-dot button on the top right, then tap Choose theme.
Google Contacts: In the app’s settings, the Theme option under the Display section.
Google Duo: The Choose theme option in the app’s settings.
Google Drive: The Choose theme option in the app’s settings.
Google Maps: Maps does not have an app-wide theme setting. However, you can force the app to use a dark interface whenever you’re using navigation, which only happens when the sun goes down or it gets dark for some other reason (like when you enter a tunnel) by default.
To do that, go into the app’s settings, tap Navigation settings, then scroll down to find the Map display tab. Here, set the Color scheme setting to Night.
Google News: The Dark theme option under the General tab of the app’s settings.
Google Play Games: In the app’s settings, the option called Use system default theme under the General tab. Hit the pencil icon next to that option to choose your preferred theme.
YouTube: The Appearance option in the General section of the app’s settings.