content: /// AppInsets represents the sizes used in this app, usually multiple of 2 in a
  /// gradually increasing way, like 2, 4, 8, 16, 32, 64, ...
  class AppInsets {
    // This class is not meant to be instantiated or extended. This constructor
    // prevents external instantiation and extension, plus it does not show up
    // in IDE code completion. We like static classes for constants because it
    // name spaces them and gives them a self documenting group and context that
    // they belong to.
    AppInsets._();
    static const double xs = 2;
    static const double s = 4;
    static const double m = 8;
    static const double l = 16;
    static const double xl = 32;
    static const double xxl = 64;
  
    // Edge padding for page content on the screen. A better looking result
    // can be obtained if this increases in steps depending on canvas size.
    // Keeping it fairly tight now, but not too small, it is a compromise for
    // both phone and larger media.
    static const double edge = 12;
  
    /// Max width of content pages with text thath should be read.
    ///
    /// The max dp width used for layout content on the screen in the available
    /// body area. Wider content gets growing side padding. Like on most
    /// web pages when they are used on super wide screen. To wide text gets
    /// difficult to read.
    static const double maxBodyWidth = 1000;
  
    /// The minimum media width treated as a phone device in this demo.
    static const double phoneWidthBreakpoint = 600;
  
    /// The minimum media height treated as a phone device in this demo.
    static const double phoneHeightBreakpoint = 700;
  }
  