Theme switch

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Theme switch</title>
  <script src="https://unpkg.com/@mahozad/theme-switch"></script>
  <link rel="stylesheet" href="styles.css">
</head>
<body>

  <theme-switch></theme-switch>

</body>
</html>

html {
  background: #fff1a4;
  /* Adopted from Bootstrap website: https://getbootstrap.com */
  background-image:
      radial-gradient(ellipse at top left,    #ddfd0d80, transparent 50%),
      radial-gradient(ellipse at center left, #d6338480, transparent 50%);
  transition: background 300ms ease;
}

html[data-theme="dark"] {
  background: #a8d8ff;
  background-image:
      radial-gradient(ellipse at top left,    #0d6efd80, transparent 50%),
      radial-gradient(ellipse at center left, #d6338480, transparent 50%);
}

theme-switch {
  --theme-switch-icon-color: #000d;
  width: 256px;
}

/* No JavaScript code used */