react-context.js

import React from "react";
import ReactDOM from "react-dom";
import "./styles.css";
const root = document.getElementById("root");

const ThemeContext = React.createContext("light");

function Toolbar(props) {
  return (
    <div>
      <Button />
    </div>
  );
}
class Button extends React.Component {
  static contextType = ThemeContext;
  render() {
    return <input type="button" value="CLick Me" theme={this.context} />;
  }
}
class App extends React.Component {
  render() {
    return (
      <ThemeContext.Provider value="dark">
        <Toolbar />
      </ThemeContext.Provider>
    );
  }
}
ReactDOM.render(<App />, root);