A user interface variation is a change to the presentation of your user interface that is based on a device configuration, such as changing the color of the background and other elements when the device is set to a dark style. A variation can apply to an element of the user interface, such removing a constraint, or to a property of a view class or constraint, such as the font for a label. You can vary:
Size or position of a view
Installation of a view
Installation of a constraint
Constraint constant
Font
Color for the font, tint, or background
Layout margins
Image file
The specific set of properties you can vary depends on the class of the element.