顶端浮动导航

设定绝对位置div后用js绑定scroll事件判断并加载div

<div id="mnav" style="width:100%;height:80px;position:fixed;top:0;left:0; background-color: #fff;border-bottom: 4px groove rgba(96,96,96,0.1);z-index: 999;" class="w1200 clearfix">

<script type="text/javascript"> 
$(window).bind('scroll', function(){
    var t = document.documentElement.scrollTop || document.body.scrollTop;

    if( t >= 900 ) { 
        $("#mnav").css("display", "inline"); 
    } 
    if(t < 900){ 
        $("#mnav").css("display", "none");
    } 

});
</script>