z-index の使用

<div id="abs1">
  <strong>DIV #1</strong>
  <br />position: absolute; <br />z-index: 5;
</div>
<div id="rel1">
  <strong>DIV #2</strong>
  <br />position: relative; <br />z-index: 3;
</div>
<div id="rel2">
  <strong>DIV #3</strong>
  <br />position: relative; <br />z-index: 2;
</div>
<div id="abs2">
  <strong>DIV #4</strong>
  <br />position: absolute; <br />z-index: 1;
</div>
<div id="sta1">
  <strong>DIV #5</strong>
  <br />位置指定なし <br />z-index: 8;
</div>

div {
  padding: 10px;
  opacity: 0.7;
  text-align: center;
}
strong {
  font-family: sans-serif;
}
#abs1 {
  z-index: 5;
  position: absolute;
  width: 150px;
  height: 350px;
  top: 10px;
  left: 10px;
  border: 1px dashed #900;
  background-color: #fdd;
}
#rel1 {
  z-index: 3;
  height: 100px;
  position: relative;
  top: 30px;
  border: 1px dashed #696;
  background-color: #cfc;
  margin: 0px 50px 0px 50px;
}
#rel2 {
  z-index: 2;
  height: 100px;
  position: relative;
  top: 15px;
  left: 20px;
  border: 1px dashed #696;
  background-color: #cfc;
  margin: 0px 50px 0px 50px;
}
#abs2 {
  z-index: 1;
  position: absolute;
  width: 150px;
  height: 350px;
  top: 10px;
  right: 10px;
  border: 1px dashed #900;
  background-color: #fdd;
}
#sta1 {
  z-index: 8;
  height: 70px;
  border: 1px dashed #996;
  background-color: #ffc;
  margin: 0px 50px 0px 50px;
}