.channel {
  width:30%;
  border:1px dotted black;
  float:left;
  height:30em; 
  margin-left:1%;
  margin-bottom:1em;
}

.channel ul {
  height:100%;
  max-height:20em;
  overflow:auto;
}

li {
  border-top:1px solid black;
}

li div.collapse {
  visibility:hidden;
  height:0;
}

li:hover div.collapse {
  visibility:visible;
  height:100%;
}