• Widget themes should have of(context) constructor.
• The underlying widgets should get the themes from the of(context) constructors.

Do

tab_bar_theme.dart

static TabBarTheme of(BuildContext build) { ... }

tabs.dart

TabBarTheme tabBarTheme = TabBarTheme.of(context);

Don't

tabs.dart

TabBarTheme tabBarTheme = Theme.of(context).tabBarTheme;