build_webstatic/webstatic.example/dist/assets/js/gcbok-theme.js

// GCBoK.WebStaticBuilder example theme script.
(function () {
  var t = localStorage.getItem('gc-theme') || 'light';
  document.documentElement.setAttribute('data-theme', t);
  var btn = document.getElementById('themeToggle');
  if (btn) btn.addEventListener('click', function () {
    var cur = document.documentElement.getAttribute('data-theme');
    var next = cur === 'light' ? 'dark' : 'light';
    document.documentElement.setAttribute('data-theme', next);
    localStorage.setItem('gc-theme', next);
  });
})();