I'm trying to follow this site: <http://jsfiddle.net/Cqp7w/>

to make a collapsible list group, which will behave exactly like "Collapse (as seen in documenatation)" part in the link I pasted above.

Yet the collapse part didn't work when I copied the corresponding html and css code to my machine, although other parts and styles work fine. I think I might need to import some other library in my html, but I couldn't figure it out by searching online, please help :)

Thanks a lot!

css & html code:

```css
body {
    padding: 2em;
}

.panel-group .list-group {
 margin-bottom: 0;
}

.panel-group .list-group .list-group-item {
 border-radius: 0;
 border-left: none;
 border-right: none;
}

.panel-group .list-group .list-group-item:last-child {
 border-bottom: none;
}
```

```html
<!doctype html>
<html>
 <head>
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" >
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap-theme.min.css">
  <link type="text/css" rel="stylesheet" href="css/style.css" media="screen" />

 </head>

 <body>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>

<h1>Collapse (as seen in documenatation)</h1>
<div class="panel-group" id="accordion">
 <div class="panel panel-default">
  <div class="panel-heading">
   <h4 class="panel-title">
    <a data-toggle="collapse" data-parent="#accordion" href="#collapseOne">Collapsible Group Item #1</a>
   </h4>
  </div>
  <div id="collapseOne" class="panel-collapse collapse in">
   <div class="panel-body">
    Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
   </div>
  </div>
 </div>
 <div class="panel panel-default">
  <div class="panel-heading">
   <h4 class="panel-title">
    <a data-toggle="collapse" data-parent="#accordion" href="#collapseTwo">Collapsible Group Item #2</a>
   </h4>
  </div>
  <div id="collapseTwo" class="panel-collapse collapse">
   <div class="panel-body">
    Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
   </div>
  </div>
 </div>
 <div class="panel panel-default">
  <div class="panel-heading">
   <h4 class="panel-title">
    <a data-toggle="collapse" data-parent="#accordion" href="#collapseThree">Collapsible Group Item #3</a>
   </h4>
  </div>
  <div id="collapseThree" class="panel-collapse collapse">
   <div class="panel-body">
    Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
   </div>
  </div>
 </div>
</div>

</body>

</html>
```