How do I fix error not found DART HTML import DART HTML <UNK>?

“error: not found: ‘dart:html’ import ‘dart:html’;” Code Answer

Built-in types and core primitives for a Flutter application . To use, import dart:ui . This library exposes the lowest-level services that Flutter frameworks use to bootstrap applications, such as classes for driving the input, graphics text, layout, and rendering subsystems.