[Typescript] Incorrect children type for CssBaseline and ScopedCssBaseline

[dfernandez-asapp]

The children property is declared as ReactElement and it should be the more general ReactNode.

• The issue is present in the latest release.
• I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior 😯

const App : React.FC = ({children}) => <CssBaseline>{children}</CssBaseline>

This example fails with the current typings. It should work.

Also PropTypes in CssBaseline uses node.

Expected Behavior 🤔

The previous example should pass the typechecking.

Steps to Reproduce 🕹

https://codesandbox.io/s/exciting-bohr-7nceq

Steps:

1. Create a TypeScript project
2. Add latest release of MUI (4.93)
3. Create a functional component like the one in the example
4. Pass children to CssBaseline or ScopedCssBaseline

Context 🔦

I'm trying to create a generic app component that does the setup of MUI theme and styles.

Your Environment 🌎

Tech	Version
Material-UI	v4.9.3
React	16.12.0
TypeScript	3.7.5
@types/react	16.9.20

[eps1lon]

You're totally right. Do you mind working on a PR?