Sample

HTML

<div id="fixed-menu">
  <div id="fixed-menu-contents">
    <a href="#" id="home"></a>
    <div class="panel-wrap">
      <a href="#" class="panel-btn">カテゴリー</a>
      <div class="panel">

    コンテンツ

      </div>
    </div>
    <div class="panel-wrap">
      <a href="#" class="panel-btn">タグ</a>
      <div class="panel">

    コンテンツ

      </div>
    </div>
  </div>
</div>

CSS

@font-face {
  font-family: 'FontAwesome';
  src: url('fonts/fontawesome-webfont.eot?v=3.0.1');
  src: url('fonts/fontawesome-webfont.eot?#iefix&v=3.0.1') format('embedded-opentype'),
    url('fonts/fontawesome-webfont.woff?v=3.0.1') format('woff'),
    url('fonts/fontawesome-webfont.ttf?v=3.0.1') format('truetype');
  font-weight: normal;
  font-style: normal;
}
#fixed-menu {
  position: fixed;
  top: 0;
  z-index: 9999;
  width: 100%;
  padding: 0;
  background: #2e4153;
}
#fixed-menu-contents {
  width: 960px;
  margin: 0 auto;
  padding: 0;
}
a#home{
  display: block;
  position: relative;
  float: left;
  width: 50px;
  height: 40px;
  border-right: 1px solid #22303d;
  border-left: 1px solid #22303d;
  color: #e4eaf0;
}
a#home:before {
  position: absolute;
  top: 10px;
  left: 15px;
  color: #cfdae4;
  font: 20px 'FontAwesome';
  content: "\f015";
}
.panel-wrap{
  position: relative;
  float: left;
  padding: 0;
  border-right: 1px solid #22303d;
}
.panel-wrap a{
  font-size: 14px;
  text-decoration: none;
}
a.panel-btn{
  display: block;
  position: relative;
  float: left;
  z-index: 100;
  padding: 0 30px 0 50px;
  color: #cfdae4;
  font-size: 14px;
  line-height: 40px;
  text-decoration: none;
}
.panel-btn:before {
  position: absolute;
  top: 10px;
  left: 20px;
  color: #cfdae4;
  font: 20px 'FontAwesome';
  content: "\f0d7";
}
a#home:hover,
a#home:hover:before,
a.panel-btn:hover,
a.panel-btn:hover:before
{
  color: #fff;
}
.panel {
  display: none;
  position: absolute;
  top: 45px;
  left: 0px;
  z-index: 1000;
  width: 200px;
  margin-left: -30px;
  padding: 10px;
  background: #fff;
  border: 5px solid #9fb5cb;
  border-radius: 3px;
  box-shadow: 0 2px 5px 1px rgba(0,0,0,.2);
}
.panel:after,#panel:before {
  content: "";
  position: absolute;
  height: 0;
  width: 0;
}
.panel:after {
  top: -35px;
  left: 35px;
  border: 15px solid transparent;
  border-bottom: 15px solid #9fb5cb;
}

jQuery

$(function() {
  $(".panel-btn").click(function(){
    var clickPanel = $("+.panel",this);
    clickPanel.toggle();
    $(".panel").not(clickPanel).slideUp(0);
    $(".panel:visible").prev().css("background","#283948");
    $(".panel:hidden").prev().css("background","#2e4153");
    return false;
  });
});