Main CSS Style
The Main CSS Style refers to the selection in the top half of the Styles drop-down menu (on the toolbar) that makes it easy to quickly change the look of your documents as they appear in Author mode and the output without having to edit the CSS stylesheets. The main CSS applies to the whole document and you can also select one or more alternate styles (listed in the bottom half of the drop-down menu) that behave like layers and are merged sequentially with the main CSS style.