我的思路：監聽scrollTop的值，變大就是向下滑，改變con_2的CSS。反之...

補充貼上代碼：

$(document).ready(function() {        var p = 0,
            t = 0;

        $(window).scroll(function(e) {
            p = $(this).scrollTop();            if (t <= p) { //下滾
                console.log("down");
            } else { //上滾
                console.log("up");
            }
            setTimeout(function() {
                t = p;
            }, 0);
        });
    });