Centering an absolute div inside a relative div

HTML-CSS
1

.parent{
position: relative;
width: 100%;
height: 100%;
}
.child {
position: absolute;
width: 60%;
height: 80%;
}
how to center?

2

This might help: https://jsfiddle.net/9j0dsovm/

3

Here is a css-tricks article on centering you might want to keep handy. It has most of the different CSS centering techniques (for the different use cases).