I want to make the horizontal boxes with the size of 200 x 200 pixel each.  I decide to use the ul li. and you guys know well that I must apply the float:left attribute to the li tag to make it horizontal. 
My problem is that when I apply the float:left to the li element, all content in li completely breaks its container. I noticed this because I append the border style to the main container and all the content is in the new line below the main container.
Here is my code
HTML :
<div class="content-box">
   <h3 class="box-header">Recent Files</h3>
   <ul class="horizontal-content">
       <li>
          <div class="filebox">
          </div>
       </li>
   </ul>
</div> 
and the css :
.content-box {
   position:relative;
   width:800px;
   border:1px solid #dadada;
   margin-left:10px;
   padding:10px;
}
ul.horizontal-content {
    list-style:none outside none;
}
ul.horizontal-content > li {
float:left;
display:block;
padding:10px;
}
.filebox {
position:relative;
padding:15px;
width:200px;
height:200px;
border:1px solid #dadada;
background-color:#ecf0f1;
}
Now you see all of my code, please help me figure out what I have done wrong.
 
     
     
     
    