Dark Mode is one of the common feature that is repeatedly come in several apps such as Google Chrome, Messenger or Google app for smartphones. The dark mode officially for whats-app has still not launched. But it is also stepped into whats-app technology worlds.

The good news is that if you are want to enable dark mode on your Android devices.
Android users who have the latest Android Q beta version can only get this feature enabled as of now.
The 'Set by Battery Saver', dark mode would be activated only when the smartphone's battery level drops below a certain point. This third option is said to be available only for smartphones running on Android 9.0 or older.

Whats-App dark theme comes with a dark grey background and the text highlighted in white color. Light theme is essentially a lighter version of the dark theme.
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Step by Step beginners guide to enable Whats-App dark mode on Android

Step 1: Go to Settings >> Display option >> Select theme >> choose Dark option.
Step 2: Once the Dark Mode is turned on, go to Settings > About phone
Step 3: Scroll down to **Build number 2.19.353** and tap on it seven times
Step 4: You will see a message pop-up saying by 'Developers options is turned on'.
Step 5: Tap on 'Override force-dark' so that you can apply the dark theme to other apps
Step 6: Dark theme is now enabled on Whats-App but the wallpaper in chat threads still                     needs to be changed to enjoy the dark mode to its fullest
Step 7: Go to WhatsApp Settings > Wallpaper > None and you are good to go
Step 8:  For iOS phones, it is necessary that the device runs on iOS 11 or later versions.
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How to enable WhatsApp dark Mode on iOS System

Step 1: Go to Settings >> General >> Accessibility >> Display Accommodations >> Invert Colours >> Smart Invert option
Step 2: You have now enabled dark theme across all the apps in your devices.
Step 3: Same as Android, you will have to choose dark or no wallpaper for Whats-App chat threads.  
Step 4:Go to WhatsApp Settings > Wallpaper > None

Whether you're using an Android or iOS device, you can enable dark mode in Whats-App by following the above-mentioned step by step.