title: How to implement Dark mode and Light Mode in flutter?
body: <p>I want to create a flutter app that has 2 light and dark mode themes that change by a switch in-app and the default theme is default android theme.<br>
  I need to pass some custom color to the fellow widget and I don't want to just config material theme.  </p>
  
  <ul>
  <li>how to detect the user device default theme?  </li>
  <li>the secend question is how to provide a theme to the whole app?  </li>
  <li>third is how change the theme with a simple switch in running time?</li>
  </ul>