问页眉分区位置固定在页面顶部，但在加载时显示页面顶部的Div。

EN

$(document).ready(function () {
    var top_fixed;
    if ($('#header-con').length > 0)
    {
        top_fixed = $('#header-con').offset().top;
    }
    $(window).scroll(function () {
        if ($('#header-con').length > 0)
        {
            $('#header-con').toggleClass('fixed', $(window).scrollTop() > top_fixed);
        }
    });
});

*{
    margin:0;
    padding:0;
}

#advert-con { color:yellow;height:130px;background:blue;width:100%;margin:0px;padding:0px;display:block; }
#header-con { height:170px;background:black;color:#fff!important;margin:0px;padding:0px; }
#content-con { height:700px;background:purple; }

.fixed {
    position: fixed;
    top: 0;
    width:100%;
}

.container{
    margin-top:130px;
    display:inline-block;
    width:100%;
}
.container:after{
    display:block;
    clear:both;
    content:"";
}

<div id="advert-con">
<h3>
    <br />
    <br />
    ADVERT DIV MUST BE OVERLAYED WITH BLACK DIV UPON SCROLLING </h3>
</div>
<!--end advert-con-->
<div id="header-con">
    <h2>
        <br />
        <br />
        HEADER DIV MUST REMAIN VISIBLE ON TOP</h2>
</div>
<!--end header-con-->
<div id="content-con">
    <h4>Content Words Text Context</h4>
</div>
<!--end content-con-->

$(document).ready(function () {
   var header = $('#header-con');
   var distanceFromTop;
   if (header.length > 0)
   {
       distanceFromTop = header.offset().top;
   }
   $(window).scroll(function () {
       if (header.length > 0)
       {
           header.toggleClass('sticky-top', $(window).scrollTop() > distanceFromTop);
       }
   });
});

.sticky-top {
    position: fixed;
    top: 0;
    width:100%;
}