Hi Cindy,
Do you mean in the Theme Options > CSS area? If so, that is fine it won’t going to be affected if you switch from parent Pro theme to child theme.
Is there any particular customization you wanted to do? Like adding tracking code or 3rd party widgets? If not, then just keep your child theme activated, at least now you have the child theme ready whenever you need it moving forward.
What Jade meant is backup your parent Pro theme (or entire site to play it safe), then move all the file customization you made on the parent theme to the child theme, base on your posts it seems you did not do any template file (coding) customization. So switching from parent theme to child theme should not be a problem on your site.
Hope this shed some lights,
Cheers!