The Icon Fit dictionary specifies how to display the button’s icon within the annotation rectangle of its widget annotation
(Optional) The circumstances under which the icon should be scaled inside the annotation rectangle:
class Numeric @.A
(Optional) The type of scaling that shall be used:
has Bool $.FB
(Optional) An array of two numbers between 0.0 and 1.0 indicating the fraction of leftover space to allocate at the left and bottom of the icon. A value of [0.0 0.0] positions the icon at the bottom-left corner of the annotation rectangle. A value of [0.5 0.5] centers it within the rectangle. This entry is used only if the icon is scaled proportionally. Defaultvalue: [0.5 0.5].