Check out example codes for "center image with position absolute". It will help you in understanding the concepts better.

Code Example 1

.wrapper img {
  left: 50%;
  transform: translate(-50%,0);
  position: absolute;
  z-index: 1 
}

Code Example 2

.center{
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    -ms-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);
}

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