There are 78 collapsible widget positions. If no widget is published to a position, it will not appear, collapsing the entire area.
The below diagram is of the Widget Variations page.
This demo includes a series of RocketTheme plugins, with theme specific styling.
This site has a range of guides to introduce you to the basics of the theme.
Radiance has valid code, based on the XHTML 1.0 Transitional standards.