.banner {
  position: fixed;
  bottom: 0;
  width: 100%;
  background: #222;
  color: #fff;
  text-align: center;
  padding: 1em;
  z-index: 9999;
  display: none;
}
.banner.visible { display: block; }
.banner button {
  margin-left: 10px;
  padding: 0.4em 0.8em;
}