Montech_Landing/apps/landing/composables/useTheme.ts

const STORAGE_KEY = "montech_theme";

/** The initial class is applied by the inline boot script in `nuxt.config.ts` before first paint. */
export function useTheme() {
  const isDark = useState("theme-dark", () => false);

  function sync() {
    isDark.value = document.documentElement.classList.contains("dark");
  }

  function toggle() {
    isDark.value = !isDark.value;
    document.documentElement.classList.toggle("dark", isDark.value);
    try {
      localStorage.setItem(STORAGE_KEY, isDark.value ? "dark" : "light");
    } catch {
      /* storage unavailable (private mode) */
    }
  }

  return { isDark, sync, toggle };
}