Google had slowly started rolling out the dark mode to its apps. Google Keep and Google Fit app had received the dark mode functionality earlier this year.
With the launch of Android 10, the company is focusing on a system-wide dark theme for which it needs all the native apps to have the theme option too. The Google App and Assitant app received the update today.
As seen from the screenshot , you get the option to enable Dark Mode always or follow the system theme.
The same goes for the Google Assistant App and once it is enabled everything darkens starting from the pop-up to the daily dashboard, the Explore section for discovering new things you can do, and all Assistant settings.
Go to the Play Store and update the apps to enjoy the dark theme yourself.