如何添加一个主题按钮，当点击时会改变页面的html背景和按钮颜色

<button id="themeButton">切换主题</button>
<div id="container">页面内容</div>

#themeButton {
  background-color: #ccc;
  color: #fff;
}

#container {
  background-color: #fff;
}

document.getElementById("themeButton").addEventListener("click", function() {
  var container = document.getElementById("container");
  var button = document.getElementById("themeButton");
  
  if (container.style.backgroundColor === "white") {
    container.style.backgroundColor = "black";
    button.style.backgroundColor = "black";
    button.style.color = "white";
  } else {
    container.style.backgroundColor = "white";
    button.style.backgroundColor = "#ccc";
    button.style.color = "white";
  }
});