center with poisition relative code example

Example 1: position absolute center

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

Example 2: vertically and horizontally center a fixed div

// you dont need to know the divs dimensions and it does not require any container divs
position: fixed; 
top: 50%;
left: 50%;
transform: translate(-50%, -50%);