Тёмный режим

<style>
body {
  padding: 25px;
  background-color: white;
  color: black;
  font-size: 25px;
}

.dark-mode {
  background-color: black;
  color: white;
}
</style>

<h2>Toggle Dark/Light Mode</h2>
<p>Click the button to toggle between dark and light mode for this page.</p>

<button onclick="myFunction()">Toggle dark mode</button>

<script>
function myFunction() {
   var element = document.body;
   element.classList.toggle("dark-mode");
}
</script>