luci-theme-alpha/luasrc/app.js

(function () {
    // your page initialization code here
    // the DOM will be available here
  
    const toggler = document.querySelector(".toggler");
    console.log(toggler);
    toggler.addEventListener(
      "click",
      function (e) {
        const element = document.querySelector(".navbar");
        element.classList.toggle("active");
      },
      false
    );
  
    const isDark = localStorage.getItem("isDark");
    if (isDark == 1) {
      const element = document.querySelector("body");
      element.classList.add("dark");
    }
    const themetoggler = document.querySelector(".themetoggler");
    themetoggler.addEventListener(
      "click",
      function (e) {
        e.preventDefault();
        const element = document.querySelector("body");
        element.classList.toggle("dark");
  
        const isDark = localStorage.getItem("isDark");
        localStorage.setItem("isDark", isDark == 1 ? 0 : 1);
      },
      false
    );
  })();