eminuxCRM/app/javascript/controllers/theme_controller.js

import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  toggle() {
    const next = document.documentElement.classList.contains("dark") ? "light" : "dark"
    this.apply(next)
  }

  apply(theme) {
    document.documentElement.classList.toggle("dark", theme === "dark")
    try { localStorage.setItem("theme", theme) } catch (_) { /* ignore */ }
    document.cookie = `theme=${theme}; path=/; max-age=31536000; SameSite=Lax`
  }
}