*,
*::before,
*::after{
  box-sizing: border-box;
}

body{
  color: white;
  text-align: center;
}

.container{
  position: relative;  
}

.z-index-auto{
  position: absolute;
  z-index: auto;
  width: 100px;
  height: 100px;
  background: rgba(0, 0, 0, 0.6);
  padding-top: 35px;
}

.z-index-0{
  position: absolute;
  z-index: 0;
  width: 300px;
  height: 300px;
  background: rgba(100, 0, 0, 0.3);
}

.z-index-1{
  position: absolute;
  z-index: 1;
  width: 200px;
  height: 100px;
  background: rgba(0, 100, 0, 0.3);
}

.z-index-2{
  position: absolute;
  z-index: 2;
  width: 200px;
  height: 100px;
  background: rgba(0, 100, 0, 0.3);
}

.z-index-100{
  position: absolute;
  z-index: 100;
  width: 200px;
  height: 100px;
  background: rgba(0, 100, 0, 0.3);
  border: 2px solid green;
}

.position1 {
  top: 0;
  left: 0;
}

.position2{
  top: 30px;
  left: 30px;
}

.position3{
  top: 70px;
  left: 70px;
}

.position4{
  top: 200px;
  left: 100px;
}

.position5{
  top: 220px;
  left: 80px;
}

.position6{
  top: 150px;
  left: 50px;
}