FoxCommerce react storefront library is a view layer which helps you show your data to client. Each component or view has strictly defined interface which it accepts for data rendering. Interface are described through flow types.
Component level customization (in runtime):
- You could override styles mapping for component
- You could override/patch existing style in css for component
SDK core built with "default" theme. Theming is done by overriding existing structure of SDK by new jsx/css/whatever. You can completely override all files if you want.
So here we get build time customization, by overriding one or multiple files in SDK.