Использование z-index для позиционирования блоков

.green-block{
    position: relative;
    background-color: green;
    width: 500px;
    height: 300px;
    margin: 0 auto;
}
.green-block h1{
    position: relative;
    color: #fff;
    text-align: center;
    padding: 100px 0 0 0;
    z-index: 2;
}
.red-block{
    width: 100px;
    height: 100px;
    background-color: red;
    position: absolute;
    left: 60px;
    top: 70px;
    z-index: 1;
}

.layer1 {
  z-index: 1;
  width: 400px;
  height: 400px;
  background: green;
  margin: 0 auto;
  position: relative;
}
.layer1 span {
  position: absolute;
  display: inline-block;
  top: 100px;
  font-size: 50px;
  font-weight: bold;
  color: #fff;
  z-index: 4;
}
.layer1 .small {
  position: absolute;
  width: 80px;
  height: 80px;
  background: lightblue;
  z-index: 2;
}
.layer1 .big {
  z-index: 4;
  position: absolute;
  width: 100px;
  height: 100px;
}
.layer1 .first {
  top: 0;
  left: 0;
}
.layer1 .second {
  top: 0;
  right: 0;
}
.layer1 .third {
  bottom: 0;
}
.layer1 .fourth {
  bottom: 0;
  right: 0;
}
.layer1 .layer3 {
  top: 100px;
  left: 100px;
  background: #fcf;
  z-index: 3;
}
.layer1 .layer4 {
  top: 150px;
  left: 150px;
  background: #fda;
}
.layer1 .layer5 {
  top: 200px;
  left: 200px;
  background: #fcf;
}