During debug mode, Flutter uses a virtual machine (VM)
to run its code in order to enable stateful hot reload,
a feature that lets you make changes to your
running code without recompilation. You’ll see
a “debug” banner in the top right-hand corner of
your app when running in this mode, to remind you that
performance is not characteristic of the finished release app.

Does Flutter use my operating system’s built-in platform widgets?

No. Instead, Flutter provides a set of widgets
(including Material Design and Cupertino (iOS-styled) widgets),
managed and rendered by Flutter’s framework and engine.
You can browse a catalog of Flutter’s widgets.

We believe that the end result is higher quality apps.
If we reused the built-in platform widgets,
the quality and performance of Flutter apps would be limited
by the flexibility and quality of those widgets.