jQuery实现产品滚动效果

html：

<div class="win_list_b">
                        <div class="scroll" style="height: 198px; overflow: hidden; position: relative;">
                            <ul class="win_list" style="position: absolute; top: -123px;">
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                                <li> **** </li>
                                                            </ul>
                        </div>
                    </div>

jQuery：

    $(function(){
        var scroll = $(".scroll"),
            list = $(".win_list");

        var height = $(".win_list_b").height(),
            listHeight = list.outerHeight();

        scroll.css({"height":height,"overflow":"hidden","position":"relative"});
        list.css({"position":"absolute","top":});

        var speed = ;

        function marquee(){
            var top = parseInt(list.css("top"));
            if(top <= height-listHeight){
                list.css({"top":});
            }else{
                list.css({"top":top-});
            }
        }
        setInterval(marquee,speed);

        var mainNav = $("#main-navbar");
        $(window).scroll(function(){
            if($(window).scrollTop()>){
                mainNav.css({"background":"#222","opacity":"0.7"});
            }else{
                mainNav.css({"background":"transparent","opacity":""});
            }
        });

    });