问如何在向下滚动时更改背景？Wordpress

EN

function scrollHandler(e)
{
refreshFocus();
} 

function refreshFocus()
{
var closest_center_dist = 99999;
var $closest_block;

var max_visible_h;
var winner;

$("div.block").each(function(ind, ele)
{

    var $block = $(ele);
    var scrollTop = $(window).scrollTop();
    var ele_y = $block.offset().top - scrollTop;
    var ele_bottom_y = $block.height() + ele_y;
    var ele_h = $block.height();
    var ele_center_y = ele_y + ele_h/2;

    var win_h = $("#win_h_ref").height()//$(window).height();
    var win_center_y = win_h/2;

    var ele_top_cutoff = Math.abs(Math.min(ele_y, 0));// from 0 to ..
    var ele_bottom_cutoff = Math.abs(Math.max(ele_y + ele_h - win_h, 0));// from 0 to ..
    var visible_ele_h = ele_h - ele_top_cutoff - ele_bottom_cutoff;


    var top_center_distance = Math.abs(ele_y - win_center_y);
    var bottom_center_distance = Math.abs(ele_bottom_y - win_center_y);

    var shortest_center_distance = Math.min(top_center_distance, bottom_center_distance);
    if(shortest_center_distance < closest_center_dist)
    {
        closest_center_dist = shortest_center_distance;
        $closest_block = $block;            
    }
});

if($closest_block)
{
    if($closest_block.size() > 0)
    {
        if($closest_block.hasClass("focus") == false)
        {
            $("div.block.focus").removeClass("focus");
            $closest_block.addClass("focus");

            $('#menu li.current').removeClass('current');
            $("#menu li a").each(function()
            {
                if($(this).attr("href") == "#"+$closest_block.attr("id"))
                {
                    $(this).closest("li").addClass("current");
                }
            });

            var $bg = $($closest_block.data("background"));
            var bg_clr = $bg.css("backgroundColor");
            $("body").css({"backgroundColor":bg_clr});

        }           
    }
}

}