StyleSheet: appshell + app consideration

[necolas]

Here's a use case I was thinking of:

1. On the server, you create an AppShell using React Native and prerender it. It will include the reset and some styles.
2. On the client, you register and run your application within an element of the static AppShell, but now StyleSheet replaces the AppShell styles.

This situation is probably OK if the client app completely replaces the styled AppShell content (i.e., both of them place content within the same element). But if the client app lives within part of the static AppShell, then running the client app will break the AppShell styles.

If the AppShell uses inline styles, I think you avoid the problem. If not, we either need to change the documentation about how to do SSR (e.g., render the shell first so StyleSheet falls back to inline styles) or rethink how StyleSheet works across server-client.