html {
  scroll-behavior: smooth;
}

* {
  box-sizing: border-box;
}

body {
  margin: 20px;
  padding: 20px;
}

footer a {
  position: fixed;
  bottom: 3em;
  right: 3em;
  background-color: rgba(255, 255, 255, 0.9);
  color: #313943;
  border: none;
  border-radius: 5px;
  padding: 1em;
  text-transform: uppercase;
  cursor: pointer;
  box-shadow: 0 0 2em 0 rgba(0, 0, 0, 0.25);
  transition: all 0.3s ease-in-out;
  display: inline-block;
  text-decoration: none;
  font-size: 0.75em;
  opacity: 0;
}

footer a:hover {
  background-color: #fff;
  padding: 1em 3em;
}

footer a.visible {
  opacity: 1;
}