html, body {
  /* Dark / Light transition */
  transition: color 0.3s ease, background-color 0.3s ease;
}

/* Dark / Light transition */
.navbar, .card, .btn {
  /* Dark / Light transition */
  transition: color 0.3s ease, background-color 0.3s ease, border-color 0.3s ease;
}

div {
    /* Dark / Light transition */
    transition: opacity 0.3s ease, background-color 0.3s ease, border-color 0.3s ease;
}