Vertically align an image inside a div with responsive height

Question

I have the following code which sets up a container which has a height that changes with the width when the browser is re-sized (to maintain a square aspect ratio).

Answer 1

With flexbox this is easy:

FIDDLE

Just add the following to the image container:

.img-container {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    display: flex; /* add */
    justify-content: center; /* add to align horizontal */
    align-items: center; /* add to align vertical */
}