How can I center image gallery within my div? - image

Question

I am trying to center a PHP generated image gallery horizontally on the page. It seems I have tried everything but nothing works! Here is a link to the page: http://rabbittattoo.com/?gallery=gallery
Here is the html that for the gallery:
<!-- Begin content -->
<div id="content_wrapper"><div class="inner">
<!-- Begin main content -->
<div id="gallery_wrapper" class="inner_wrapper portfolio"><div class="standard_wrapper small"><br class="clear"></br><br></br>
<!-- Begin portfolio content -->
<div class="one_fourth" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div><div class="one_fourth" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div><div class="one_fourth" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div><div class="one_fourth last" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div><br class="clear"></br><div class="one_fourth" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div><div class="one_fourth" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div><div class="one_fourth" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div><div class="one_fourth last" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div><br class="clear"></br><div class="one_fourth" style="margin-right:24px;margin-bottom:24px;margin-top:-20px"></div></div>
<!-- End main content -->
And the associated CSS:
#content_wrapper .inner .inner_wrapper.portfolio {
padding: 10px 0px 0px;
position: relative;
left: -10px;
}
#content_wrapper .inner .inner_wrapper {
margin-top: 28px;
}
#content_wrapper .inner .inner_wrapper {
width: 91%;
margin-left: 5.5%;
padding: 10px 0px 25px;
background: none repeat scroll 0% 0% transparent;
margin-top: 30px;
}
#gallery_wrapper {
width: 100%;
margin: 0px auto;
}
And the PHP:
$pp_gallery_style = get_option('pp_gallery_style');
if($pp_gallery_style == 'f')
{
include_once(TEMPLATEPATH.'/gallery-f.php');
exit;
}
if(!isset($hide_header) OR !$hide_header)
{
get_header();
}
$caption_class = "page_caption";
$portfolio_sets_query = '';
$custom_title = '';
if(!empty($term))
{
$portfolio_sets_query.= $term;
$obj_term = get_term_by('slug', $term, 'photos_galleries');
$custom_title = $obj_term->name;
}
else
{
$custom_title = get_the_title();
}
/**
* Get Current page object
**/
$page = get_page($post->ID);
/**
* Get current page id
**/
if(!isset($current_page_id) && isset($page->ID))
{
$current_page_id = $page->ID;
}
if(!isset($hide_header) OR !$hide_header)
{
?>
<div class="wrapper_shadow"></div>
<div class="page_caption">
<div class="caption_inner">
<div class="caption_header">
<h1 class="cufon"><?php echo the_title(); ?></h1>
</div>
</div>
</div>
</div>
<!-- Begin content -->
<div id="content_wrapper">
<div class="inner">
<!-- Begin main content -->
<div id="gallery_wrapper" class="inner_wrapper portfolio">
<div class="standard_wrapper small">
<br class="clear"/><br/>
<?php
}
else
{
echo '<br class="clear"/>';
}
?>
<?php echo do_shortcode(html_entity_decode($page->post_content)); ?>
<!-- Begin portfolio content -->
<?php
$menu_sets_query = '';
$portfolio_items = 0;
$portfolio_sort = get_option('pp_gallery_sort');
if(empty($portfolio_sort))
{
$portfolio_sort = 'DESC';
}
$args = array(
'post_type' => 'attachment',
'numberposts' => $portfolio_items,
'post_status' => null,
'post_parent' => $post->ID,
'order' => $portfolio_sort,
'orderby' => 'date',
);
$all_photo_arr = get_posts( $args );
if(isset($all_photo_arr) && !empty($all_photo_arr))
{
?>
<?php
foreach($all_photo_arr as $key => $portfolio_item)
{
$image_url = '';
if(!empty($portfolio_item->guid))
{
$image_id = $portfolio_item->ID;
$image_url[0] = $portfolio_item->guid;
}
$last_class = '';
$line_break = '';
if(($key+1) % 4 == 0)
{
$last_class = ' last';
if(isset($page_photo_arr[$key+1]))
{
$line_break = '<br class="clear"/><br/>';
}
else
{
$line_break = '<br class="clear"/>';
}
}
?>
<div class="one_fourth<?php echo $last_class?>" style="margin-right:24px;margin-bottom:24px;margin-top:-20px">
<a title="<?php echo $portfolio_item->post_title?>" href="<?php echo $image_url[0]?>" class="one_fourth_img" rel="gallery" href="<?php echo $image_url[0]?>">
<img src="<?php echo get_stylesheet_directory_uri(); ?>/timthumb.php?src=<?php echo $image_url[0]?>&h=370&w=350&zc=1" alt=""/>
</a>
</div>
<?php
echo $line_break;
}
//End foreach loop
?>
<?php
}
//End if have portfolio items
?>
</div>
<!-- End main content -->
<br class="clear"/><br/>
</div>
<?php
if(!isset($hide_header) OR !$hide_header)
{
?>
</div>
<!-- End content -->
<?php get_footer(); ?>
<?php
}
?>
I have tried centering by adjusting the margins but is had no effect. Can anyone tell me what I am doing wrong? Thank you in advance for your help!