To style the product page you don't have to do much. The system is created so that your product page inherits the styling from the other text styles in Global Styling. This way you assure a coherent design all over your shop. If you have chosen a template as a starting point, all texts will already be styled and customized, and why the product page inherits, it will automatically be styles as well.
If you make text changes in the Global Design, these will automatically be applied on the product page as well.
1. Overview: Normal page vs. Product page