React.js, React hooks, CSS

This is my first React app so pardon the unstructured layout.

• Are there any resources or recommendation to structure an app like this when using react? I added all of my CSS to one style sheet App.css and was wondering if I should also separately add my page CSS and form CSS in different files.
• I noticed that react injects the code within a div element so I was wondering if I still should add <header> <main> and <footer> tags within react? Let me know if you have any suggestions/tips/spotted bugs, I'd greatly appreciate it!