function CenterItem(theItem){
    var winHeight=$(window).height();
    var windowMiddle=winHeight/2;
    var itemMiddle=$(theItem).height()/2;
    var theMiddle=windowMiddle-itemMiddle;
    if(winHeight>$(theItem).height()){ //vertical
        $(theItem).css('top',theMiddle);
    } else {
        $(theItem).css('top','0');
    }
}
$(document).ready(function() {
    CenterItem('.centered');
});
$(window).resize(function() {
    CenterItem('.centered');
});