.reference {
  cursor: pointer;
  padding: 18px;
  width: 100%;
  text-align: left;
  outline: none;
  transition: 0.4s;
  border: 1px solid;
}


.active, .reference:hover {
  background-color: #555;
}


.panel {
  padding: 0 18px;
  background-color: white;
  display: none;
  overflow: hidden;
}