CSS - 具有/固定位置的Child Div相对Div父级 - jQuery Sticky Header

Question

我遇到元素定位问题。我有子位置（#mainNav，.metaNav），其位置为：fixed但这会导致它们忽略具有overflow：hidden（＃container2）的父div容器。在保持溢出的同时保持定位相同的任何方法：隐藏为父div？

http://jsfiddle.net/chapster82/kmszt/3/

CSS

#container2 {
    height: 2400px;
    width: 980px;
    margin-right: auto;
    margin-left: auto;
    position: relative;
    overflow: hidden;
}
#dashboardNav {
    -moz-box-shadow: 1px 0 3px rgba(0,  0,  0,  0.3);
    -webkit-box-shadow: 1px 0 3px rgba(0,  0,  0,  0.3);
    box-shadow: 1px 0 3px rgba(0,  0,  0,  0.3);
    background-color: #35478C;
    border-right: 1px solid #171717;
    position: relative;
    left: 0;
    bottom: 0;
    width: 62px;
    text-transform: uppercase;
    z-index: 100;
    font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
    font-size: 62.5%;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
    float: left;
    height: 100%;
}
#dashboardNav #mainNav {
    -moz-transition: margin-top 0.4s cubic-bezier(0.2,  0.3,  0.05,  1);
    -webkit-transition: margin-top 0.4s cubic-bezier(0.2,  0.3,  0.05,  1);
    -o-transition: margin-top 0.4s cubic-bezier(0.2,  0.3,  0.05,  1);
    -ms-transition: margin-top 0.4s cubic-bezier(0.2,  0.3,  0.05,  1);
    transition: margin-top 0.4s cubic-bezier(0.2,  0.3,  0.05,  1);
-webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
}
#dashboardNav .metaNav {
    position: fixed;
    bottom: 0;
}

HTML

<div id="container2">
   <div id="dashboardNav">
     <nav id="mainNav">
       <a class="previous" data-view="previous">Go Back</a>
       <a class="overview" data-view="overview">Overview</a>
       <a class="social" data-view="social">Search</a>         
     </nav>
     <nav class="metaNav">
        <a class="help">Help</a>
     </nav>
   </div>
  <div id="column1"></div>
</div>

感谢您的帮助。