useContext.ts

type Theme = 'light' | 'dark';
const ThemeContext = createContext<Theme>('dark');

const App = () => (
  <ThemeContext.Provider value="dark">
    <MyComponent />
  </ThemeContext.Provider>
)

const MyComponent = () => {
  const theme = useContext(ThemeContext);
  return <div>The theme is {theme}</div>;
}