The ability to create Responsive Projects was introduced last June with the arrival of Adobe Captivate 8. During the development process, you can basically create and work on multiple screen sizes (called break points) in one Captivate project. When you publish the responsive project, the learner will automatically be served the break point appropriate for the device they're using.
As I've created more and more Responsive Projects, one of the big concerns is to ensure the fonts and font sizes used in each break point is appropriate for the display size. For instance, I might want my font size to be 14 points in my Primary Break Point, 12 points in my Tablet Break Point, and a bit smaller in my Mobile Break Point.
While I could manually change the font formatting used on my slides, Break Point by Break Point, if I've got a lot of slides, that means I've got a ton of work to do.
As an alternative to manually formatting the slide objects, visit the Object Style Manager (via the Edit menu). Select an Object Style and in the Text Format area, notice that there's a Break Points drop-down menu. The menu contains three options: Primary,Tablet, and Mobile.
Select each Break Point in turn and set the desired Font Family, Size, Format, Color, etc. When finished, click the OK button and you'll see your changes immediately on the project's three Break Points.