Use the subproperty editor to set a property
In the Properties panel, you can set properties in several ways. The simplest way is to type a value, select a button, or select a value from a drop-down list. More complex properties use the subproperty and collection editors. You can also use advanced property options to data-bind, template-bind, or apply a resource to a property.
The following procedure shows you how to use a subproperty editor to set the Effect property.
For information about how to add multiple effects to an object, see Apply, modify, or delete an effect.
Select an object on the artboard, such as a button or a rectangle.
Under Appearance in the Properties panel, click New next to the Effect property.
In the Select Object dialog box, select the DropShadowEffect, and then click OK.
The area underneath the Effect property displays the subproperty editor, which contains the properties that you can set for the DropShadowEffect object (such as the BlurRadius property). Subproperty editors are identified by a dark border. You can expand and collapse the subproperty editor to modify your settings by using the drop-down arrow that appears on the left side of the Effect property.