Pass props between siblings (React) - reactjs

Question

I've got this functional component
import React from 'react'
function Header(){
return(
<div className='header'>
<h2>Logo</h2>
<p>Log In</p>
</div>
)
}
export default Header
When I will clicked on "Log In" I want to change my background-color in this class in class 'MainContainer'. Im a beginner in React. How Can I do it?
import React from 'react'
import RegistrationForm from '../LoginPage/RegistrationForm'
import './style2.scss'
class Main extends React.Component{
constructor(param){
super(param)
}
render(){
return(
<div className="mainContainer">
<RegistrationForm/>
</div>
)
}
}
export default Main
EDIT: Here is the class where I called this classes:
import React from 'react'
import Header from './components/LoginPage/Header'
import Main from './components/LoginPage/Main'
function App() {
return (
<div>
<Header/>
<Main/>
</div>
)
}
export default App;

Answer 1

Props can be passed from parent to child, not between siblings. So make a state in the App component and pass it down to Main and Header.
App
function App() {
const [loggingIn, setLoggingIn] = React.useState(false);
return (
<div>
<Header setLoggingIn={setLoggingIn} />
<Main loggingIn={loggingIn} />
</div>
)
}
Main
class Main extends React.Component{
constructor(param){
super(param)
}
render(){
return(
<div className="mainContainer" style={{ background: this.props.loggingIn ? 'red' : 'inherit' }}>
<RegistrationForm/>
</div>
)
}
}
Header
function Header({ setLoggingIn }){
return(
<div className='header'>
<h2>Logo</h2>
<p onClick={() => setLoggingIn(true)}>Log In</p>
</div>
)
}