Cannot figure CSS selectors

I’ve been working on this for about 5 hours now and can’t wrap my head around what needs to be in each field.

I can’t say what I’ve tried so far since I’ve tried so many different options.

Can someone help me out?

<div class="content">

 <?php if (have_posts()) : ?><?php $count = 0; ?>
 <?php while (have_posts()) : the_post(); ?><?php $count++; ?><?php if ($count == 1) : ?>

 <div id="post_holder">

<div class='thumb'>
 <a href="<?php the_permalink(); ?>" rel="bookmark">
 <?php if(has_post_thumbnail()) { $image_src = wp_get_attachment_image_src( get_post_thumbnail_id(),'thumbname' ); echo '<img src="' . $image_src[0] . '" width="726px"/>'; } ?></a>
</div><!-- thumb -->

</div><!--post_holder-->

<?php else : ?>

<div id="posts_bellow">

<div class='thumb'>
  <a href="<?php the_permalink(); ?>" rel="bookmark">
  <?php if(has_post_thumbnail()) { $image_src = wp_get_attachment_image_src( get_post_thumbnail_id(),'thumbname' ); echo '<img src="' . $image_src[0] . '" width="726px" />'; } ?></a>
</div>

</div><!--posts_bellow-->

<?php endif; ?>
<?php endwhile; ?>

<div id='pagination'>
<div class="nav-previous alignleft"><?php next_posts_link( 'Older posts' ); ?></div>
<div class="nav-next alignright"><?php previous_posts_link( 'Newer posts' ); ?></div>
</div>

<?php else : ?>
<p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
<?php endif; ?>

</div><!-- content -->

I’ve changed my pagination because of this..
prior it was:

<?php if(function_exists('wp_pagenavi')) { wp_pagenavi(); } else {?>
<div class="navhold"><?php posts_nav_link(' · ', '<< Recent', 'More >>'); ?></div>
<?php wp_link_pages('before=<div id="page-links">&after=</div>'); ?>
<?php } ?>
<?php else : ?>
<div id="notfound_holder"><h1>Not Found</h1><p>Sorry, but you are looking for something that isn't here.</p></div>
<?php endif; ?>

What exactly am I to put in callback?
I can’t figure what exactly my A link is when it is using php for pagination (not a php pro)

My site is http://www.devilonadinosaur.com

http://ww.wp.xz.cn/plugins/infinite-scroll/