Try something like this. This should center any huge element in the middle vertically and horizontally with respect to its parent no matter both of their sizes.
.parent {
position: relative;
overflow: hidden;
//optionally set height and width, it will depend on the rest of the styling used
}
.child {
position: absolute;
top: -9999px;
bottom: -9999px;
left: -9999px;
right: -9999px;
margin: auto;
}