lesson-10/example6-1.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
  <style type="text/css" media="screen">
body{
  background: white;
}
.layer {
  width: 200px;
  height: 200px;
  position: absolute;
  /* border: 1px solid #FEFEFE; */
  border-radius: 10px;
}

.highlight {
  box-shadow: 0px 0px 6px rgba(35,173,255,1);
  border
}
  </style>
</head>
<body>

  <div class="layer" style="left: 10px; top:10px; background: AntiqueWhite "></div>
  <div class="layer" style="left: 30px; top:30px; background: Aquamarine"></div>
  <div class="layer" style="left: 50px; top:50px; background: BlueViolet"></div>
  <div class="layer" style="left: 70px; top:70px; background: Brown"></div>
  <div class="layer" style="left: 90px; top:90px; background: BurlyWood"></div>
  <div class="layer" style="left: 110px; top:110px; background: Chartreuse"></div>
  <div class="layer" style="left: 130px; top:130px; background: DarkBlue"></div>
  <div class="layer" style="left: 150px; top:150px; background: DarkSalmon"></div>
  <div class="layer" style="left: 170px; top:170px; background: DarkSeaGreen "></div>

<script>
function getEl(e) {
  var el = e.target;
  if (e.target.classList.contains('layer')) {
    return el
  }
}

var z = 0
document.documentElement.addEventListener('mouseover', function(e) {
  var el = getEl(e)
  if (!el) return
  el.classList.add('highlight')
})

document.documentElement.addEventListener('mouseout', function(e) {
  var el = getEl(e)
  if (!el) return
  el.classList.remove('highlight')
})

document.documentElement.addEventListener('click', function(e) {
  var el = getEl(e)
  if (!el) return
  el.style.zIndex = ++z
})
</script>
</body>
</html>