There are three basic controls:
Default Centre Button displays the currently-selected image that will be used for the Dock's
default central button control and provides the ability to change it using the ellipsis button (…).
Normal Opacity allows you to alter the opacity (or transparency) of the image. Move the slider to
the left to increase transparency or to the right to increase opacity.
Normal Size allows you to change the size of the Dock's Centre button. You will not be able to
select a size greater than the visible area of your screen - height being the governing factor.
