smiley.html

<!-- in head -->
<style>
body.clicked {
  background: #7f1d26;
}
.smiley {
  position: fixed;
  top: 1rem;
  right: 1rem;
  width: 1rem;
  height: 1rem;
  line-height: 1rem;
  font-size: 1rem;
  transition-duration: .5s;
}

body.clicked .smiley {
  transform: rotate(360deg) scale(2);
}

</style>

<!-- in body -->
<div class="smiley">😎</div>

<script>
jQuery('.smiley').on('click', function() {
  jQuery('body').toggleClass('clicked');
});
</script>