How do you vertically center an image in ui-content ?

How do you vertically center an image in ui-content ?

My ui-content is VERY simple, it's just a single image, really, nothing else, just a single image.

<div data-role="main" class="ui-content">
      <div style="text-align:center;"><img src="images/home_logo_600px.svg" class="fullscreen"></div>
</div>

The CSS for "fullscreen" is just a simple:
.fullscreen
{
    max-width:100%;
    max-height:100%;
}

So here is the question, by doing text-align:center; I have centered the image that is now filling up the width of the whole screen on portrait mode thanks to max-width:100%;

How do I center the image vertically in ui-content ?
Thanks.