Hi Cindy,
Welcome to the forums

.
You might want to explore
Global Project Linking.
In Effect, create your stylesheet in the master project.
Next, create a new import file in the Project Organiser. If you are only interested in the stylesheet you can limit the linking to .css files. When finished setting your import options you click import.
Then you can create your topics using the linked stylesheet. Set the topics to use the imported spreadsheet. (If it has imported correctly you should see it in the Content Explorer -> Resources -> Stylesheets folder).
HTH