向上或向下滚动后转换固定div的top属性

Question

我正在尝试复制此网站上找到的已修复所有渠道div的功能：http://thenextweb.com/

我有一个固定的div，我想要在顶部：50px当标题在屏幕上（标题是50px）然后一旦标题不再在屏幕上，固定的div位于顶部的窗口。

我想我可能不得不使用jQuery，但我真的不确定。寻找一些意见，并希望在纯CSS中做到这一点。

我的代码：

HTML

<div id ="wrapper">

    <!--Start header-->
    <div id ="header">

        <!--Start main-list-->
        <div id="main-list">
            <ul>
                <li id ="hidden-burger"><img src="../images/nextimages/burger.png"></li>
                <li id ="logo"><a href=""><img src="../images/nextimages/tnwlistlogo.png"/></a></li>
                <li id ="blog"><a href="">Blog</a></li>
                <li id ="other-main-list"><a href="">Conference</a></li>
                <li id ="other-main-list"><a href="">103 Deals</a></li>
                <li id ="other-main-list"><a href="">Pro</a></li>
            </ul>
        </div>
        <!--End main-list-->

        <!--Start social list-->
        <div id ="social">
          <ul>
            <li><div class="fb-like" data-href="https://www.facebook.com/thenextweb" data-layout="button" data-action="like" data-show-faces="false" data-share="false"></div></li>
            <li><a href="https://twitter.com/TheNextWeb" class="twitter-follow-button" data-show-count="false" data-show-screen-name="false">Follow</a></li>
            <li><a href="http://thenextweb.com/feed?token=116910" id="rss"></a></li>
            <li id ="down-arrow"><i class="fa fa-sort-desc"></i></li>
            <li id="hidden-follow">Follow<i class="fa fa-sort-desc"></i></li>
            <li id ="user"><i class="fa fa-user"></i></li>
            <li id ="info"><i class="fa fa-info-circle"></i></li>
            <li id ="search"><i class="fa fa-search"></i></li>
            <input id ="search-input" name="search" placeholder ="Search..." type="text"></input>
         </ul>

        </div>
        <!--End Social List-->

    </div>
    <!--End header-->

<!--Start stream-->
<div id="stream">

    <!--Start top-stream-->
    <div id="top-stream">

        <ul>
            <li id="latest">
                <i class="fa fa-clock-o"></i> Latest
            </li>
            <li id="popular">
                <i class="fa fa-fire"></i> Popular
            </li>
        </ul>

        <!--Start all-channels-->
        <div id="all-channels">

            <span>All Channels</span> <i class="fa fa-sort-desc"></i>

        <select>

            <option value ="all">All Channels</option>

            <optgroup label="Channels">
                <option value="apps">Apps</option>
                <option value="creativity">Creativity</option>
                <option value="dd">Design & Dev</option>
                <option value="entrepreneur">Entrepreneur</option>
                <option value="gadgets">Gadgets</option>
                <option value="Insider">Insider</option>
                <option value="lifehacks">Lifehacks</option>
                <option value="media">Media</option>
                <option value="Offers">Offers</option>
                <option value="Shareables">Shareables</option>
                <option value="socialmedia">Social Media</option>
            </optgroup>

        </select>
        </div>
        <!--END all-channels-->
    </div>
    <!--END top stream-->

        <!--Start stream-list-->
        <div id="stream-list">
            <ul>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
                <li id="stream-item"></li>
            </ul>
        </div>
        <!--END stream list-->

    <!--Start stream footer-->
    <div id ="stream-footer">
        <ul>
        <li>About</li>
        <li>Goodies</li>
        <li>Advertise</li>
        <li>Privacy</li>
        <li>ToS</li>
        </ul>
    </div>
    <!--END stream footer-->

</div>

CSS

#wrapper {
    height:100%;
    width:100%;
    padding:0;
    margin:0;
}
#header{
    width:100%;
    max-width:100%;
    height:3em;
    border-bottom: 2px solid #d9e0e2;
    min-width:320px;
}
#hidden-burger{
    width:24px;
    height:24px;
    display:none;
    padding-top:.3em;
    float:left;
}
#main-list{
    width:45%;
    float:left;
}
#main-list li{
    float:left;
    height:3em;
    vertical-align:middle;
}
#main-list ul{
    height::3em;
    padding:0;
    margin:0;
    list-style-type:none;
}
#logo {
    margin-right:.875em;
}
#blog a{
    color:#FF3C1F;
    display:block;
    margin-right:.5em;
    line-height:2.9em;
    text-decoration:none;
    font-size:1em;
    font-weight:400;
    text-transform:capitalize;
    font-family:'Fjalla One', Arial, Helvetica, sans-serif;
    text-transform:uppercase;
    border-bottom:2px solid #FF3C1F;
}
#other-main-list a{
    display:block;
    margin-right:.875em;
    line-height:2.9em;
    text-decoration:none;
    font-size:1em;
    color:#879096;
    font-weight:400;
    opacity:.6;
    text-transform:capitalize;
    font-family:'Fjalla One', Arial, Helvetica, sans-serif;
    text-transform:uppercase;
}

#other-main-list a:hover{
    color:#FF3C1F;
    border-bottom:2px solid #FF3C1F;
    opacity:1;
}
#main-list img{
    padding-top:4px;
    padding-left:5px;
}

#social{
    width:30em;
    float:right;
}
#social ul {
    float:right;
    padding:0;
    margin:0;
    list-style-type:none;
}
#social li{
    margin-right:.3em;
    float:left;
    vertical-align:middle;
    height:3em;
    padding-top:.75em;
}

#social i{
    width:24px;
    height:3em;
    margin-right:.5em;
}
#social i:hover{
    color:#FF3C1F;
    cursor:pointer;
}


#social img{
    width:24px;
    height:24px;
}

#social i:first-child{
    margin-left:.875em;
}
#rss{
    display: block;
    border-right:none;
    height: 20px;
    width: 20px;
    background: #f80;
    color: #fff;
    border-radius: 2px;
    top: 0;
    line-height: 20px;
    font-size: 14px;
    text-align: center;
    text-indent: 2px;
    border: 1px solid #dd7600;
    background-image:url(../images/nextimages/rss.png);
}

#down-arrow, #user, #info{
    border-right:1px solid #F2F2F2;
}

#hidden-follow{
    display:none;
    font-size:10px;
    font-weight:800;
    text-transform:uppercase;
    margin-top:.75em;
    color:#4e5860;
    font-family:'Source Sans Pro', sans-serif;
}
#hidden-follow:hover{
    color:#FF3C1F;
    cursor:pointer;
}
#search-input {
    width:25%;
    background-color: #f7f9f9;
    border-radius: 3px;
    float:left;
    display: inline-block;
    font-size: 14px;
    line-height: 20px;
    margin-top:5px;
    outline: 0;
    padding: 8px 8px 6px 8px !important;
    border: 1px solid #d9e0e2 !important;
    box-shadow: none;
    font-family:'Source Sans Pro', sans-serif;
    font-weight:200;
    padding-left:50px;
}

#stream {
    margin-bottom: 1.25em;
    position: fixed;
    padding: 0 0 .75em 0;
    font-weight: 400;
    float: left;
    z-index: 88;
    background: #fff;
    border-right: 1px solid #d9e0e2;
    height: 100%;
    width: 325px;
    -webkit-font-smoothing: antialiased;
}
#top-stream{
    border-bottom: 1px solid #d9e0e2;
    box-shadow: 0 2px 0 rgba(217,224,226,0.2);
    padding: 20px 12px;
    color:#4e5860;
    font-size:.875em;
    font-weight:800;
    font-family:'Source Sans Pro', sans-serif;
    text-transform:uppercase;
    height:8.5em;
}
#top-stream ul{
    list-style-type:none;
    padding:0;
    margin:0;
}
#top-stream li{
    float:left;
    padding:1em;
    border: 1px solid #d9e0e2;
    vertical-align:middle;
    border-radius:1px;
    cursor:pointer;
    box-shadow: 0 2px 0 rgba(217,224,226,0.2);
    border-radius:.25em;
    margin:0;
    color:#4e5860;
    font-size:.875em;
    font-weight:800;
    font-family:'Source Sans Pro', sans-serif;
    text-transform:uppercase;
}
#latest{
    border-right:none;
    width:12em;
    text-align:center;
    background-color:#F8F9FA;
}
#popular{
    width:12em;
    text-align:center;
}
#all-channels {
    width:24em;
    margin-top:1em;
    background-color: #ff3c1f;
    border-radius: .25em;
    color: #fff;
    font-family: 'Source Sans Pro',sans-serif;
    font-size: .875em;
    font-style: normal;
    line-height: 36px;
    float:left;
    position:relative;
    cursor:pointer;
}
#all-channels span{
    float:left;
    padding-left:1em;
}
#all-channels i{
    float:right;
    padding:.875em;
}
#all-channels select{
    height:100%;
    width:100%;
    position:absolute;
    left:0;
    margin-top:.875em;
    opacity:0;
    cursor:pointer;
}
#stream-list{
    width: auto;
    height: 100%;
    overflow:hidden;
    overflow:scroll;
}
#stream-item{
    height:5em;
    padding: .813em;
    border-bottom: 1px solid rgba(217,224,226,0.4);
}
#stream-footer{
    background-color: #fff;
    border-top: 1px solid #d9e0e2;
    bottom: 0;
    box-shadow: 0 -2px 0 rgba(217,224,226,0.2);
    font-size: .875em;
    left: 0;
    padding: .75em 0 1em;
    position: fixed;
    text-align: center;
    width: 324px;
    color: #ff3c1f;
    font-family:'Source Sans Pro', sans-serif;
}
#stream-footer ul{
    margin:0;
    padding:0;
    list-style-type:none;
    text-align:center;
}
#stream-footer li{
    display:inline-block;
    padding:.5em;
}
#stream-footer li:hover{
    cursor:pointer;
}

Answer 1

这里是demo

基本上，当滚动位置高于div位置时，您需要更改position属性。