css transition nested

HTML

<div id="box">
  <span>Box</span>
  <div id="overlay">Overlay</div>
</div>

CSS

#box {
  position: relative;
  width: 200px;
  padding: 9px 15px;
  background-color: #ED8029;
  color: white;
  border-radius: 5px;
  -webkit-transition: background-color 10s;
  -moz-transition: background-color 10s;
  -o-transition: background-color 10s;
  -ms-transition: background-color 10s;
  transition: background-color 10s;
}

#box:hover {
  background-color: #A7B526;
}

#overlay {
  display: none;
  background-color: lightblue;
}

#box:hover #overlay {
  display: block;
  position: absolute;
  top: 36px;
  left: 0;
  right: 0;
  height: 50px;
  border-radius: 5px;
  background-color: lightgreen;
}