You can single-source styles through the use of style sheet mediums.
One use for a medium is to have one group of style settings for online formats (DotNet Help, HTML Help, WebHelp, WebHelp Plus, WebHelp AIR, WebHelp Mobile) and a different group of settings for print-based formats (Adobe PDF, XHTML, Microsoft XPS, Microsoft Word, Adobe FrameMaker). Therefore, you could use one medium for your online targets and use another medium for PDF and your other print-based targets.
example
Let's say you have text hyperlinks that are shown in blue font with an underline. That may be fine for Target A, but let's say you want this style to appear in black font with no underline for Target B. The solution is to use a style sheet medium.
Suppose Target A is using the "default" medium, where the blue underline properties are specified. With the properties for Target A already set, you now need to specify style properties for Target B. Therefore, in the Stylesheet Editor, instead of selecting the "default" medium, you can select another medium (e.g., the "print" medium) and change the properties for the style to black with no underline. It's the same style sheet and the same style that you are working with. The only difference is that one medium is telling Flare to display that content in blue with an underline, and the other medium is telling it to use black font with no underline. With Target A using the default medium and Target B using the other medium, the content will display appropriately in each output.