Google is working on Dark Mode for Google Search in Chrome on Android, but if you prefer doing your searches in the Google Search app you no longer have to wait, as Google has started rolling out Dark Mode for the app on iOS and Android.
The feature is currently rolling out, and if you have Android 10 or iOS 13 the app should automatically detect your theme preference and switch as needed.
If not you can make the switch in Settings, and also switch back if you don’t like the new look.
The feature has been in the beta app for some time, so should be pretty perfect now. It is rolling out now but may take a week to reach all handsets.