.banner {
  overflow-y: hidden;
  max-height: 0;
  background: lightgrey;
  padding-left: 1em;
  
  -webkit-transition-property: all;
  -webkit-transition-duration: 2s;
  -moz-transition-property: all;
  -moz-transition-duration: 2s;
  -ms-transition-property: all;
  -ms-transition-duration: 2s;
  transition-property: all;
  transition-duration: 2s;
}

.banner.closed {
  max-height: 0;
}

.banner.opened {
  max-height: 100px;
}