dark_mode.js

if (getCookie("dm")===""){
  document.cookie = "dm=1";
} else if (getCookie("dm") === "1" && !document.getElementById('dark_mode_link')) {
  setDarkMode();
} else if (getCookie("dm") === "0") {
  if (document.getElementById("dark_mode"))
    document.getElementById("dark_mode").checked = false;
  setLightMode();
}

function on_dark_mode() {
  dark_mode_toogle = document.getElementById("dark_mode");
  // get <link rel="stylesheet" href="main.css">
  // maincss = document.getElementById("main_css");

  /* if (darkmode.checked == true){
    // change to dark_mode.css
    $('link[href="main.css"]').attr('href','dark_mode.css');
  } else {
    // change to main.css
    $('link[href="dark_mode.css"]').attr('href','main.css');
  } */

  if((dark_mode_toogle.checked == true && !document.getElementById('dark_mode_link'))) {
    setDarkMode();
    document.cookie = "dm=1";
  }
  else {
    setLightMode();
    document.cookie = "dm=0";
  }
}

function setDarkMode() {
  var dark_mode_link = document.createElement('link');
  dark_mode_link.rel = 'stylesheet';
  dark_mode_link.href = 'dark_mode.css';
  dark_mode_link.id = 'dark_mode_link';
  document.head.appendChild(dark_mode_link);
}

function setLightMode() {
  var dark_mode_id = document.getElementById("dark_mode_link");
  dark_mode_id.parentNode.removeChild(dark_mode_id);
}