Cannot enable Gradle's offline mode on Android Studio 3.6
From the Android Studio 3.6 new features blog post:
New location to toggle Gradle's offline mode To enable or disable Gradle's offline mode, first select View > Tool Windows > Gradle from the menu bar. Then, near the top of the Gradle window, click Toggle Offline Mode Gradle offline button in the Gradle panel..
Here is the link -- hope that helps!
To enable or disable Gradle's offline mode, select View > Tool Windows > Gradle from the menu bar and near the top of the Gradle window, click Toggle Offline Mode 
To clarify it. In your Android Studio...
View > Tool Windows > Gradle
And then this...
And this...
