Appearances
The appearances section in the theme file is where all the styles and properties that apply to the widgets are defined. Each widget has an appearance name (corresponds to the AppearanceKey property exposed by the server-side control) that selects which section of the theme applies to the widget.
The appearances are organizes in a hierarchical structure:
See Elements section for a detailed explanation of the theme structure.
Components refer to child widgets that compose a larger widget. The name of the component is the name used by the parent widget to refer to the child.
The component entry in the Theme is identical to the Appearance entry. A component can include other components in a recursive structure.
In the image above, you can see that the Button appearance contains a component named Icon. Each component has a set of states and for each state it has styles and properties.