html, body {
  height: 100%;
  margin: 0;
  overflow: hidden;
}

body {
  transition: background 0.8s ease;
  font-family: sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  color: white;
  text-align: center;
}

body::before {
  content: '';
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  z-index: -1;
  background-size: 200% 200%;
  background-position: left center;
  transition: background 0.6s ease, background-position 1.5s ease;
}

body.shifted::before {
  background-position: right center;
}

.flip-on-hover {
  display: inline-block;
  transition: transform 0.6s ease;
  transform-style: preserve-3d;
  cursor: pointer;
  perspective: 1000px;

  user-select: none;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
}


.flip-on-hover.flipped {
  transform: rotateX(180deg);
}