Good day.
I know that if you want to absolute center a div, you do this:
blahblah
As the width and height are fluid, you need to go with javascript or jQuery. Just add the below code in head tag. (The below example is in javascript)
and your css would be something like this:
#parent{
max-width: 500px;
max-height: 500px;
background-color:green;
position:absolute;
top: 50%;
left: 50%;
/* width: 10%;
height: 10%; */
}
To test, give width: 10%; and height: 10%
Working Fiddle