如何在重新点击后将深色主题更改为浅色主题[重复]

body.darktheme{
  color:white;
  background: #444;
}

<button onclick="document.body.classList.toggle('darktheme')">Toggle dark theme</button>

<h1>Hello World!</h1>

const myBtn = document.getElementById("toggle-theme");
const body = document.body;
const welcome = document.getElementById("txtt")

myBtn.addEventListener("click", function(){
   body.classList.toggle('dark')
    
}) 

body { background-color: white; color: black;}
body #txtt { color: black; }
body.dark { background-color:black; color: white}
body.dark #txtt { color: white }

<button id="toggle-theme">toggle</button>
<div id="txtt">Welcome</div>

const myBtn = document.getElementById("myBtn");
const body = document.body;
const welcome = document.getElementById("txtt");

let isDarkTheme = false; // flag variable to track the current theme state

myBtn.addEventListener("click", function() {
  if (isDarkTheme) {
    // switch to light theme
    body.style.backgroundColor = "white";
    body.style.color = "black";
    welcome.style.color = "black";
  } else {
    // switch to dark theme
    body.style.backgroundColor = "rgb(17, 17, 17)";
    body.style.color = "white";
    welcome.style.color = "white";
  }
  
  isDarkTheme = !isDarkTheme; // toggle the theme state
});

<button id="myBtn">Toggle dark theme</button>
<h1 id="txtt">Hello!<h1>

const myBtn = document.getElementById("darktheme");
const body = document.body;
const welcome = document.getElementById("txtt")

myBtn.addEventListener("click", function(){
    if(body.style.backgroundColor==="rgb(17, 17, 17)")
    {
      body.style.backgroundColor = "rgb(256, 256, 256)";
      body.style.color = "black";
      welcome.style.color = "black";
    }
    else
    {
      body.style.backgroundColor = "rgb(17, 17, 17)";
      body.style.color = "white";
      welcome.style.color = "black";
    }
}) 

<button id="darktheme">darktheme</button>
<input type="text" id="txtt"/>