how to get an absolute object to be in the center of page? code example

Example 1: position absolute center

.child {
    position: absolute;
    top: 50%;  
    left: 50%; 
    transform: translate(-50%, -50%);
}

Example 2: center image with position absolute

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

Example 3: position absolute center

position: absolute;
margin-left: auto;
margin-right: auto;
left: 0;
right: 0;
text-align: center;