Unable to make feature image float left on categoty page

I am trying to make a child theme for Twenty Twelve with a custom category page that looks something like this: http://laurenconrad.com/blog/cat/primp. Specifically, I would like to have the feature image to the left and the post title and excerpt to the right. I’ve tried scouring the internet for solutions but I just keep ending up with the text above or below the feature image. Below is my current attempt that is not working

I’ve tried creating a div class with this in the style.css:

.featuredImage {
	float: left;
}

In my functions.php, I have created a new thumbnail size for the category pages:

if ( function_exists( 'add_theme_support' ) ) {
	add_theme_support( 'post-thumbnails' );
        set_post_thumbnail_size( 624, 9999 ); // default Post Thumbnail dimensions
}

if ( function_exists( 'add_image_size' ) ) {
	add_image_size( 'category-thumb', 300, 9999 ); //300 pixels wide (and unlimited height)
}

Then in my content.php, I have the following:

<?php if ( is_search() || is_archive() || is_author() || is_tag() ) : // Only display Excerpts  ?>
			<div class="featuredImage">
				<a href="<?php the_permalink(); ?>"><?php the_post_thumbnail('category-thumb'); ?></a>
			</div>
			<h2><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
            <?php the_excerpt(); ?>

I’m very inexperienced at this, so I could easily be missing something simple. I believe I’ve searched and tried many of the methods that I’ve found with no avail, but if there’s a link to a solution that would also be much appreciated. Thank you for any help in advance.