Design-Time style sheets allow you to show or hide design applied by a CSS style sheet as you work in a Dreamweaver document. For example, you can use this option to include or exclude the effect of a Macintosh-only or a Windows-only style sheet as you design a page.
Design-Time style sheets only apply while you are working in the document; when the page is displayed in a browser window, only the styles that are actually attached to or embedded in the document appear in a browser.
To use a Design-time style sheet, follow these steps.