Hi Derek - yes, the styling and symbology is done outside of Experience Builder. Rather it is done in the Map Viewer, saved, then brought into the application framework as a Data Source.
The Power Plants - 100 MW or more feature layer's item details page is here and is generated from the following agencies - "Mapping Resources implemented as part of the North American Cooperation on Energy Information (NACEI) between the Department of Energy of the United States of America, the Department of Natural Resources of Canada, and the Ministry of Energy of the United Mexican States."