#bttn {
  display: inline-block;
  background-color: #000;
  width: 50px;
  height: 50px;
  text-align: center;
  border-radius: 5px;
  position: fixed;
  bottom: 30px;
  right: 10px;
  transition: background-color .3s,
    opacity .5s, visibility .5s;
  opacity: 0;
  visibility: hidden;
  z-index: 1000;
}

/*
 * Pure CSS up-chevron.
 * Replaces the Font Awesome glyph:
 *   content: "\f077";
 *   font-family: FontAwesome;
 */
#bttn::after {
  content: "";
  position: absolute;
  top: 20px;
  left: 18px;
  width: 12px;
  height: 12px;
  border-top: 3px solid #fff;
  border-left: 3px solid #fff;
  transform: rotate(45deg);
  box-sizing: border-box;
}

#bttn:hover {
  cursor: pointer;
  background-color: #137EAA;
  text-decoration: none;
}

#bttn:active {
  background-color: #555;
}

#bttn.show {
  opacity: 1;
  visibility: visible;
}

/* Styles for the content section */

@media (min-width: 500px) {
  #bttn {
    margin: 10px;
  }
}