How to set the post featured image to 100% width

Replies: 0

Hi. I manually added the featured post image to all posts, adding the following code in single.php:

<!-- START mod to show the feature image on posts. --!>
 <?php
 if (  !(has_post_format(  array( 'audio', 'aside', 'chat', 'gallery', 'image', 'link', 'quote', 'status', 'video' ) ) )): // Image ?>

<div class="post-format">
	<div class="image-container">
		<?php if ( has_post_thumbnail() ) {
		the_post_thumbnail('thumb-large');
			$caption = get_post(get_post_thumbnail_id())->post_excerpt;
			if ( isset($caption) && $caption ) echo '<div class="image-caption">'.$caption.'</div>';
		} ?>
	</div>
</div>

<?php endif; ?>

<!-- END mod for featured image --!>

The image shows normally, like this:
http://demo-hueman.presscustomizr.com/2013/07/16/image-format-post/

But I would like the image to have 100% width. Basically like this:

http://mychristina.com.br/musica/discografia/albuns/christina-aguilera-album/

Can you help me?

I appreciate any help that I can get.

Thanks.