What Are Style Environments?
Style environments allow you to define variations in the appearance of a style. Such variations allow you to use one style sheet in several different ways without having to make several similar style sheets. You can have any number of environments in a style sheet.
For example, the default style sheet included with Mathematica has the following four style environments.
Working: designed for on-screen use
Presentation: designed for presentations, either from a computer or printed on transparencies
Condensed: designed for viewing on a small screen or printing on less paper
Printout: designed for optimal printing of the notebook
Style environments for a particular style sheet are defined in the style sheet itself.
In the style sheets included with Mathematica, the environment definition cells are grouped with the main style definition cell. The cell group is closed so that only the main style definition cell is seen. When you double-click the closed cell group bracket, three other cells appear that define the Presentation, Condensed, and Printout versions of that cell style.