Pure CSS expanding folder tree menu

I'm absolutely fascinated by the new opportunities offered by CSS3 and I never stop testing these new features. In this article you'll see how to create a pure CSS folder tree menu. Let's see the details.

We start with the following markup structure:

<ul id="folder">
   <li>
       <a href="#sub-1">1</a><span>Folder 1</span>
           <ul id="sub-1">
               <li>A</li>
               <li>B</li>
               <li>C</li>
           </ul>
  </li>
  <li>
    <a href="#sub-2">1</a><span>Folder 2</span>
           <ul id="sub-2">
               <li>D</li>
               <li>E</li>
               <li>F</li>
           </ul>
 </li>
</ul>​

As you can see, each outer link has an hash that points to the innermost list. By doing so, we can use the :target pseudo-class to create our expanding effect:

#folder {
    margin: 2em;
}

#folder > li {margin-bottom: 0.5em;}

#folder > li > a {
    display: inline-block;
    width: 16px;
    height: 16px;
    text-indent: -1000em;
    background: url(icons.png) no-repeat 0 -32px;
    margin-right: 5px;
}

#folder > li > a:active {background-position: 0 -16px;}



#folder > li > a + span {
    display: inline-block;
    height: 16px;
    line-height: 16px;
    padding-left: 20px;
    font-weight: bold;
    background: url(icons.png) no-repeat 0 0;
}

#folder > li ul {
    margin-left: 2.5em;
    line-height: 1.4;
    display: none;
}

#folder > li ul:target {
    display: block;
}
​

You can see the demo below.

Demo

Live demo