What programming paradigm does Flutter’s framework use?

Flutter is a multi-paradigm programming environment.
Many programming techniques developed over the past few decades
are used in Flutter. We use each one where we believe
the strengths of the technique make it particularly well-suited.
In no particular order:

The primary paradigm used by Flutter is that of using
small objects with narrow scopes of behavior, composed together to
obtain more complicated effects, sometimes called
aggressive composition. Most widgets in the Flutter widget
library are built in this way. For example, the Material
TextButton class is built using
an IconTheme, an InkWell, a Padding,
a Center, a Material,
an AnimatedDefaultTextStyle, and a ConstrainedBox.
The InkWell is built using a GestureDetector.
The Material is built using an
AnimatedDefaultTextStyle,
a NotificationListener, and an AnimatedPhysicalModel.
And so on. It’s widgets all the way down.