Please read the documentation in here or contact Luiz Filipe da Silva

Hey, Godstime Onyibe! Currently, the code is stable and works fine.

Add the script before the closing tag body, as it follows:

  ...
  <script src="cdn.jsdelivr.net/gh/luizfilipezs/dark-theme-switc…"></script>
  <script type="text/javascript">
    new ThemeSwitcherGenerator().init();
    // or
    new ThemeSwitcher(someElement).init();
  </script>
</body>

Remember that what the package does is inverting the colors. So, to change the background of your body tag, as an example, you must give it a background color.