Flutter is a framework for building cross-platform applications
that uses the Dart programming language.
To understand some differences between programming with Dart
and programming with Javascript, 
see Learning Dart as a JavaScript Developer.

One of the fundamental differences between
designing a web layout and a Flutter layout,
is learning how constraints work,
and how widgets are sized and positioned.
To learn more, see Understanding constraints.

The examples assume:

The HTML document starts with <!DOCTYPE html>, and the CSS box model
for all HTML elements is set to border-box,
for consistency with the Flutter model.

    
{
    box-sizing: border-box;
}

In Flutter, the default styling of the ‘Lorem ipsum’ text
is defined by the bold24Roboto variable as follows,
to keep the syntax simple: