FunctionContextComponent.js

import {useTheme,useThemeUpdate} from "../ThemeContext";

export default function FunctionContextComponent(){
  const darkTheme = useTheme()
  const toggleTheme = useThemeUpdate()
  const themeStyles = {
    backgroundColor:darkTheme?'#333':'#CCC'
  }
  return (
    <>
      <button onClick={toggleTheme}>toggle Theme</button>
      <div style={themeStyles}>Function Theme</div>
    </>
  )
}