CSS centering of an image not working

Question

I'm trying to center an image (forces.png) horizontally using margin-left and margin-right auto but the image remains left-aligned. My site is http://goo.gl/cHO1u What's wrong with the code I'm using? Thanks

HTML:

<div class="section" id="presentation">
<div id="presentation-highlevel">
<p>NOTRE ENTREPRISE</p>
<p>ddfdsfdsfdsfdsjfl dfljdsfdsfjdsjfdlksj dfljdslfjldsjflkdsjflsjfdls ldf,dlsmjfdsjfsdmfjdmsjfms dfmdsfjmdsjfmdsjfmdsjfdlms mkdfmksdmfkdmsfkdsfdsmfkmldskf dfmdmkfmdkfmdlskf dfkdmfkdmkfmdskf dfmkdsmfkdsmkfmdskfdms dskfdsmkfdsmkfmdsfkd </p>
</div>
<div id="presentation-highlights"><img src="images/forces.png" alt="Picture" /></div>
</div><!--END page1-->

CSS:

#presentation
{
    height:1300px;
    background:#afc9ff; 
  background: url(../images/norway-landscape60.jpg) no-repeat center fixed; 
  -webkit-background-size: cover; /* pour Chrome et Safari */
  -moz-background-size: cover; /* pour Firefox */
  -o-background-size: cover; /* pour Opera */
  background-size: cover; /* version standardisée */
}

#presentation-highlights

{
width: 100%;
display: block;
margin-left:auto;
margin-right:auto;
}

Solution

#presentation-highlights {
text-align:center;
width:100%;
display:block;
margin:auto;
}