There are three basic controls:
Background Image displays the currently-selected image that will be used for the Dock's
background 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 background. You will not be able to
select a size greater than the visible area of your screen - height being the governing factor.
If the Dock Shape is a Circle, then this control adjusts both the height and width of the
background. However, if the Dock Shape is an Ellipse, this control adjusts the width and Circle
Dock calculates the new height using the aspect ratio of the Ellipse's innermost "ring" (set in Dock
Shape)
