Center Featured Image? With no themes e.g. custom website blog

Hi,

I am very new to blogs and wordpress and need a little direction.

Basically, I am using wordpress as CMS just for the blog page on a website and I am having some trouble with a few styling things.

First problem I am having is making all Feature Images Centered. Currently, by default they are displayed on the left.

My blog page:

<?php
/* Short and sweet */
define('WP_USE_THEMES', false);
require('./wp-blog-header.php');
?>

<div class="wrapper">
    	<div class="inner-wrapper" id="blog">

    	<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

        <?php the_post_thumbnail();?>

        <h2><a href="<?php the_permalink(); ?>" rel="bookmark"><?php the_title() ;?></a></h2>

		<div id="date"><?php the_time('j F Y'); ?></div> 

        <!--below -- add additional when only viewing post-->
        <?php if ( is_single() ) {

   			the_content();

			}
			else {

   			the_excerpt();
			echo '<div class="line-breaker" id="blog-line"></div>';

			}?>

<?php endwhile; else: ?>

	<p>Sorry, no posts to list</p>

<?php endif; ?>

    </div>
 </div>