function vpWidth() {
    return window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth;
}
function vpHeight() {
    return window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
}
function load(){
    var top;
    var left;
    if(vpHeight() >= 521){
        top = (vpHeight()-521)/2;
    } else {
        top = 0;
    }
    if(vpWidth() >= 771){
        left = (vpWidth()-771)/2;
    }else{
        left = 0;
    }
    $("#main_content").css("left", left);
    $("#main_content").css("top", top);
}