old_contents: import React from 'react';
  
  const App = () => <h1>Hello, world!</h1>;
  
  export default App;
  
new_contents: import React from 'react';
  import Container from './Container';
  import Header from './Header';
  import Logo from './Logo';
  
  const App = () => (
    <Header>
      <Container>
        <Logo href="#">C</Logo>
      </Container>
    </Header>
  );
  
  export default App;
  
subject: Add initial header structure to the App component