Responsive design problem Plumbelt-Lite

Hi everybody,
I’m using Plumbelt Lite responsive design template for a portfolio website. I have an issue about the view in mobile devices. I made an adjustment to eliminate the sidebar on the right of some pages and I created a page2.php with this code:

<?php /* Template Name: Nosidebar */ ?>
	<?php

	/*
	* 	The template for displaying Page.
	*
	* 	@package plumbelt-lite
	*/

	get_header();

	?>

	<section class="content">

		<div class="container">

			<div class="main-wrapper-fullwidth">

				<h1>

					<?php the_title(); ?>

				</h1>

				<?php

				if ( have_posts() ) {

					while ( have_posts() ) {

						the_post(); ?>

						<article>

							<?php the_content(); ?>

							<?php
								if ( comments_open() || '0' != get_comments_number() ) :
									comments_template();
								endif;
							?>
						</article>

						<?php }

				}

				?>

			</div><!--/.main-wrapper-->

			<div class="clear"></div>

		</div><!--/.container-->

	</section><!--/.content-->

	<?php get_footer(); ?>

and added in style.css some code like this:

#content-fullwidth {
width: 850px;
float: left;
padding-bottom: 5px;
}

No problem when I try to visualize the pages on desktop, but on mobile I see that the content goes over the background and you can’t visualize the entire page without go orizzontally on the page. I guess I forgot to add some key code for responsive design.
This is the link to the page: http://www.guerriarchitettura.it/lavori/concorsi/progetto-antiquarium/
Thanks for any help.