Generated cascading style sheets overview
When you format items in a web page, Microsoft Expression Web produces that formatting by generating new styles in an internal cascading style sheet (CSS) or modifying existing styles in the CSS.
You can work with the styles that Expression Web generates for you by using the same CSS tools that you use to design and apply CSS, including the Apply Styles, Manage Styles, and CSS Properties task panes, the Style toolbar, and the New Style and Modify Style dialog boxes. In addition, the CSS tab in the Page Editor Options dialog box provides several options for the styles that Expression Web generates for you. For more information, see Set preferences for generated CSS.
Expression Web generates and modifies styles for you in Auto mode (default) or Manual mode. No matter which mode you choose, when you format an item that doesn't have a style, Expression Web generates and applies a new style for you. For example, if you select a paragraph of plain text in your web page and apply color to the text by using the Font Color button in the Common toolbar, Expression Web creates a new style and applies it to the text to format its color. If you then format another property of that same paragraph of text, such as the paragraph's font-family, Expression Web adds a new property declaration to the generated style it just created.
In Manual mode, you have additional control provided by the Style Application toolbar. You can have the new property declaration added to a different style instead, including a new style, a different generated style, or a style that you created. For more information, see Design generated styles in manual mode.
If you're new to authoring CSS, use Auto mode. If you're an experienced CSS author that can write your own CSS, use Manual mode to streamline your design process.