anchor.diff:  
   class PaperStyleSheet extends css.StyleSheet {
     build() => [
  -      css.rule('.Paper_shadow', [
  -        css.position('absolute'),
  -        css.top(0),
  -        css.left(0),
  -        css.right(0),
  -        css.bottom(0),
  -        css.borderRadius('inherit'),
  -        css.transition('box-shadow 0.5s $swiftEaseInOut'),
  -      ]),
  +      css.rule('.Paper', [
  +        css.position('relative'),
   
  -      css.rule('.Paper', [
           css.rule('&.round', [
             css.borderRadius('3px')
           ]),
  +
           css.rule('&.circle', [
             css.borderRadius('50%')
           ]),
  
positive.code:         css.rule('&.z5 > .Paper_shadow', [
            paperShadow(5)
          ])
        ])
      ];
  }
  
negative.code:       ..classes.add('Paper');
  
      shadowElement.classes.add('Paper_shadow');
  
      element
        ..append(shadowElement);
    }
  
    v.VRootDecorator<html.DivElement> build() =>
  