.vjs-marker
{
  position:absolute;
  background:red;
  width:5px;
  height:110%;
  top:-5%;
  z-index:30;
  margin-left:-3px;
}

.vjs-marker:hover span 
{
  opacity:1;
}

.vjs-marker span
{
  position:absolute;
  bottom:15px;
  opacity:0;
  margin-left:-20px;
  z-index:90;
  background:rgba(0,0,0,.8);
  padding:8px;
  font-size:10px;
  width: 15em;
}