The app also served a pop-up at the bottom of the screen informing that this feature is available now.
Although Google has not officially announced the feature, this mode is now available for Android.
Apparently, the color isnt really black but it is more like a dark grey.
Step 2: Then, tap on your profile icon that appears on the right top corner.
Step 3: Go to tweaks > General.
Step 4: Tap on the toggle for Dark theme to enable it.
Step 5: Tap on the back button, the theme is automatically saved.
source: www.techworm.net