Container

color:

red

width:

4000

height:

50

),

To learn how constraints work in Flutter,
see Understanding constraints.

Design system

Because Flutter targets multiple platforms, your app doesn’t need
to conform to any design system.
Though this guide features Material widgets,
your Flutter app can use many different design systems:

Custom Material widgets

Community built widgets

Your own custom widgets

Cupertino widgets that follow Apple’s Human Interface Guidelines

If you’re looking for a great reference app that features a
custom design system, check out Wonderous.

UI Basics