backend-server-v2/web/static/vendor/theme.js

(function () {
  var STORAGE_KEY = "theme";
  var root = document.documentElement;
  var mediaQuery = window.matchMedia("(prefers-color-scheme: dark)");

  function getStoredTheme() {
    var value = null;
    try {
      value = localStorage.getItem(STORAGE_KEY);
    } catch (e) {
      value = null;
    }
    return value === "dark" || value === "light" ? value : null;
  }

  function getPreferredTheme() {
    return mediaQuery.matches ? "dark" : "light";
  }

  function applyTheme(theme) {
    root.classList.toggle("dark", theme === "dark");
  }

  function currentTheme() {
    return root.classList.contains("dark") ? "dark" : "light";
  }

  function setStoredTheme(theme) {
    try {
      localStorage.setItem(STORAGE_KEY, theme);
    } catch (e) {
      // localStorage may be unavailable in private mode or blocked contexts.
    }
  }

  function updateToggleState(theme) {
    var button = document.getElementById("themeToggle");
    if (!button) return;

    var isDark = theme === "dark";
    button.setAttribute("aria-pressed", isDark ? "true" : "false");
    button.textContent = isDark ? "Light mode" : "Dark mode";
  }

  function applyInitialTheme() {
    var stored = getStoredTheme();
    applyTheme(stored || getPreferredTheme());
  }

  window.toggleTheme = function toggleTheme() {
    var next = currentTheme() === "dark" ? "light" : "dark";
    applyTheme(next);
    setStoredTheme(next);
    updateToggleState(next);
  };

  window.initThemeToggle = function initThemeToggle() {
    updateToggleState(currentTheme());
  };

  if (typeof mediaQuery.addEventListener === "function") {
    mediaQuery.addEventListener("change", function (event) {
      if (getStoredTheme()) return;
      var theme = event.matches ? "dark" : "light";
      applyTheme(theme);
      updateToggleState(theme);
    });
  } else if (typeof mediaQuery.addListener === "function") {
    mediaQuery.addListener(function (event) {
      if (getStoredTheme()) return;
      var theme = event.matches ? "dark" : "light";
      applyTheme(theme);
      updateToggleState(theme);
    });
  }

  applyInitialTheme();
})();