CommandStation-EX/_static/dark_mode_js/theme_switcher.js

const createThemeSwitcher = () => {
  let btn = document.createElement('BUTTON');
  btn.className = 'theme-switcher';
  btn.id = 'themeSwitcher';
  btn.innerHTML =
    '<i id=themeMoon class="fa fa-moon-o"></i><i id=themeSun class="fa fa-sun-o"></i>';
  document.body.appendChild(btn);

  if (localStorage.getItem('theme') === 'dark') $('#themeMoon').hide(0);
  else $('#themeSun').hide(0);
};

$(document).ready(() => {
  createThemeSwitcher();
  $('#themeSwitcher').click(switchTheme);

  $('footer').html(
    $('footer').html() +
      '<a href="https://github.com/MrDogeBro/sphinx_rtd_dark_mode">Dark theme</a> provided by <a href="http://mrdogebro.com">MrDogeBro</a>.'
  );
});

const switchTheme = () => {
  if (localStorage.getItem('theme') === 'dark') {
    localStorage.setItem('theme', 'light');
    document.documentElement.setAttribute('data-theme', 'light');

    $('#themeSun').fadeOut(200, () => {
      $('#themeMoon').fadeIn(200);
    });
  } else {
    localStorage.setItem('theme', 'dark');
    document.documentElement.setAttribute('data-theme', 'dark');

    $('#themeMoon').fadeOut(200, () => {
      $('#themeSun').fadeIn(200);
    });
  }
};