Never mind- I just found the answer
HERE.
The instructions in the Manager say: "Enter the path to your CSS file that you wish to use within the editor. The best way to enter the path is to enter the path from the root of your server, for example: /assets/site/style.css. If you do not wish to load a stylesheet into the editor, leave this field blank."
Now, obviously I’m not the only one who was confused about what this is and what it’s for. Maybe this needs to be worded differently? For instance:
"Leaving this field blank will allow the editor to work normally. If you wish to use a different stylesheet specific to your content within the content editor, enter the path here. The best way to enter the path is to enter the path from the root of your server, for example: /assets/site/style.css."