.z10-parent
  .z10 z-index 10, z-index 10, z-index 10, z-index 10, z-index 10, z-index 10
.z1 z-index 1, z-index 1, z-index 1, z-index 1, z-index 1, z-index 1, z-index 1, z-index 1, z-index 1, z-index 1, z-index 1, z-index 1, z-index 1
  
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body {
  background: #ccc;
}

.z10-parent {
  -webkit-overflow-scrolling: touch;
  overflow: auto;
}

.z10 {
  background: #fff;
  z-index: 10;
  width: 300px;
  height: 100px;
  position: absolute;
  left: 0;
  top: 0;
}

.z1 {
  color: white;
  position: absolute;
  width: 150px;
  height: 300px;
  position: absolute;
  background: #000;
  left: 0;
  top: 0;
}
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