Is it possible to assign style to one particular category?

This search:
https://www.google.com/search?q=wordpress+style+posts+differently

found, among others, this:
https://lorelle.wordpress.com/2007/09/06/using-wordpress-categories-to-style-posts/

Thank you so much! Doing this by ways of the category slugs is a great idea. However, I am having trouble with figuring out where (and how) to insert this
line of code (per the instructions from Lorelle),

<div class="post<?php the_category_unlinked(' '); ?>">

into my index.php file so it will create this HTML code for a post:
<div class="post opensource feature">

I’m using K2, so the index.php looks like this:

<?php get_header(); ?>	

<div class="content">

<div id="primary-wrapper">
	<div id="primary">

		<div id="notices"></div>
		<a></a>

		<?php if ( '1' == get_option('k2rollingarchives') ): ?>
		<div id="dynamic-content">

			<?php include(TEMPLATEPATH . '/rollingarchive.php'); ?>

		</div> <!-- #dynamic-content -->
		<?php else: ?>
		<div id="current-content" class="hfeed">

			<?php include(TEMPLATEPATH . '/theloop.php'); ?>

		</div> <!-- #current-content -->

		<div id="dynamic-content"></div>
		<?php endif; ?>
	</div> <!-- #primary -->
</div> <!-- #primary-wrapper -->

	<?php get_sidebar(); ?>

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

<?php get_footer(); ?>

I have really tried, but nothing seems to work. I got my formatting to show up in the header, page background, and entire content wrapper. Just not inside the individual post, and I am new at this, so I have run out of options. Once again, help is really appreciated.

Not sure where the template tag, the_content(), is in that theme, maybe theloop.php but you’ll probably want it just before that…

Well the simple answer would be make a category-x.php file which is the same as the php file which currently governs that particular category. Now make a file called header2.php, copy your current header, but change the link for the stylesheet to the stylesheet you want. Now go back to your category-x.php file and replace <?php get_header(); ?> with <?php include ('header2.php'); ?>

That should work, I’m going to do the same thing as you on my site which I’m currently redesigning. That’s the technique I figured I would use. If it doesn’t work or you would like me to make my instructions clearer, just say.

Yes, it was supposed to go into the theloop.php file in K2! Thank you so much!!

It now looks like this (I hope I inserted the line at the right place, it works in Firefox and Safari on a Mac, but I have to wait until tomorrow until I can test it on IE):

<?php
	// This is the loop, which fetches entries from your database.
	// It is a very delicate piece of machinery. Be gentle!

	// Get core WP functions when loaded dynamically
	if ( isset($_GET['k2dynamic']) ):

		// Check for CGI Mode
		if ( 'cgi' == substr( php_sapi_name(), 0, 3 ) ):
			require_once( preg_replace( '/wp-content.*/', '', __FILE__ ) . 'wp-config.php' );
		else:
			require_once( preg_replace( '/wp-content.*/', '', $_SERVER['SCRIPT_FILENAME'] ) . 'wp-config.php' );
		endif;

		if ( $_GET['k2dynamic'] != 'init' ):
			// Send the header
			header('Content-Type: ' . get_bloginfo('html_type') . '; charset=' . get_bloginfo('charset'));

			// K2 Hook
			do_action('k2_dynamic_content');

			// Initialize the Loop
			query_posts( $_GET );
		endif;
	?>

<div id="dynamictype" class="<?php k2_body_class(); ?>">

<?php endif;

	// Debugging
	if ( isset($_GET['k2debug']) ):
		echo '<div class="alert">';
		echo '<b>SQL:</b><br />'; var_dump($wp_query->request);
		echo '<b>Query:</b><br />'; var_dump($wp_query->query);
		echo '</div>';
	endif;

	// Get the asides category
	$k2asidescategory = get_option('k2asidescategory');
	$k2rollingarchives = get_option('k2rollingarchives');

	/* Check if there are posts */
	if ( have_posts() ):
		/* Post index for semantic classes */
		$post_index = 1;
?>

	<?php /* Top Navigation */ if ( ('0' == $k2rollingarchives) or is_single() ): k2_navigation('nav-above'); endif; ?>

	<?php /* Headlines for archives */ if ( ( ! is_single() and ! is_home() ) or is_paged() ): ?>
		<div class="page-head">
			<h2><?php

			// Load the post for date archive titles
			if ( is_date() ): the_post(); endif;

			// Figure out what kind of page is being shown
			if ( is_category() ):
				if ( get_query_var('cat') != $k2asidescategory ):
					printf( __('Archive for the \'%s\' Category','k2_domain'), single_cat_title('', false) );
				else:
					echo single_cat_title();
				endif;

			elseif ( is_day() ):
				printf( __('Daily Archive for %s','k2_domain'), get_the_time( __('F jS, Y','k2_domain') ) );

			elseif ( is_month() ):
				printf( __('Monthly Archive for %s','k2_domain'), get_the_time( __('F, Y','k2_domain') ) );

			elseif ( is_year() ):
				printf( __('Yearly Archive for %s','k2_domain'), get_the_time( __('Y','k2_domain') ) );

			elseif ( is_search() ):
				printf( __('Search Results for \'%s\'','k2_domain'), attribute_escape( get_search_query() ) );

			elseif ( function_exists('is_tag') and is_tag() ):
				if ( function_exists('single_tag_title') ):
					printf( __('Tag Archive for \'%s\'','k2_domain'), single_tag_title('', false) );
				else:
					printf( __('Tag Archive for \'%s\'','k2_domain'), attribute_escape( get_query_var('tag') ) );
				endif;

			elseif ( is_author() ):
				printf( __('Author Archive for %s','k2_domain'), get_author_name( get_query_var('author') ) );

			elseif ( is_paged() and ( intval(get_query_var('paged')) > 1) ):
				 _e('Archive','k2_domain');
			endif;

			if ( ( intval( get_query_var('paged') ) > 1 ) and ( '0' == $k2rollingarchives ) ):
				printf( '<span class="archivepages">' . __('Page %1$s of %2$s', 'k2_domain') . '</span>', intval( get_query_var('paged')), $wp_query->max_num_pages);
			endif;

			// Reset the post for date archive titles
			if ( is_date() ): rewind_posts(); endif;

			?></h2>
		</div>
	<?php endif; ?>

	<?php /* Start the loop */ while ( have_posts() ): the_post(); ?>

		<div id="post-<?php the_ID(); ?>" class="<?php echo attribute_escape(k2_post_class($post_index++, in_category($k2asidescategory), false)); ?>">
			<div class="entry-head">
				<h3 class="entry-title"><a href="<?php the_permalink(); ?>" rel="bookmark" title='<?php printf( __('Permanent Link to "%s"','k2_domain'), wp_specialchars(strip_tags(the_title('', '', false)),1) ); ?>'><?php the_title(); ?></a></h3>

				<div class="entry-meta">
					<?php
						printf(	__('<span class="meta-start">Published</span> %1$s %2$s %3$s<span class="meta-end">.</span>','k2_domain'),

							'<div class="entry-author">' .
							sprintf(  __('<span class="meta-prep">by</span> %s','k2_domain'),
								'<address class="vcard author"><a href="' . get_author_posts_url(get_the_author_ID()) .'" class="url fn" title="'. sprintf(__('View all posts by %s','k2_domain'), attribute_escape(get_the_author())) .'">' . get_the_author() . '</a></address>'
							) . '</div>',

							'<div class="entry-date">' .
							( function_exists('time_since') ?
									sprintf(__('%s ago','k2_domain'),
										'<abbr class="published" title="' . get_the_time('Y-m-d\TH:i:sO') . '">' . time_since(abs(strtotime($post->post_date_gmt . " GMT")), time()) . '</abbr>') :
									sprintf(__('<span class="meta-prep">on</span> %s','k2_domain'),
										'<abbr class="published" title="' . get_the_time('Y-m-d\TH:i:sO') . '">'. get_the_time( get_option('date_format') ) . '</abbr>')
							) . '</div>',

							'<div class="entry-categories">' .
							sprintf( __('<span class="meta-prep">in</span> %s','k2_domain'),
								k2_nice_category(', ', __(' and ','k2_domain'))
							) . '</div>'
						);
					?>

					<?php /* Comments */ comments_popup_link('0&nbsp;<span>'.__('Comments','k2_domain').'</span>', '1&nbsp;<span>'.__('Comment','k2_domain').'</span>', '%&nbsp;<span>'.__('Comments','k2_domain').'</span>', 'commentslink', '<span>'.__('Closed','k2_domain').'</span>'); ?>

					<?php /* Edit Link */ edit_post_link(__('Edit','k2_domain'), '<span class="entry-edit">','</span>'); ?>

					<?php /* Tags */ if (is_single() and function_exists('UTW_ShowTagsForCurrentPost')) { ?>
						<span class="entry-tags"><?php _e('Tags: ','k2_domain'); ?><?php UTW_ShowTagsForCurrentPost("commalist"); ?>.</span>
					<?php } elseif (is_single() and function_exists('the_tags')) { ?>
						<span class="entry-tags"><?php the_tags(__('Tags: ','k2_domain'), ', ', '.'); ?></span>
					<?php } ?>
				</div> <!-- .entry-meta -->
			</div> <!-- .entry-head -->

			<div class="entry-content">
			  <div class="post<?php the_category_unlinked(' '); ?>"> <!-- category styles -->
			  <?php the_content(sprintf(__('Continue reading \'%s\'', 'k2_domain'), the_title('', '', false))); ?>

				<?php wp_link_pages('before=<p class="page-links"><strong>' . __('Pages:','k2_domain') . '</strong>&after=</p>'); ?>
			</div> <!-- .entry-content -->
</div>
		</div> <!-- #post-ID -->

	<?php endwhile; /* End The Loop */ ?>

<?php /* If there is nothing to loop */ else: define('K2_NOT_FOUND', true); ?>

	<div class="hentry four04">

		<div class="entry-head">
			<h3 class="center"><?php _e('Not Found','k2_domain'); ?></h3>
		</div>

		<div class="entry-content">
			<p><?php _e('Oh no! You\'re looking for something which just isn\'t here! Fear not however, errors are to be expected, and luckily there are tools on the sidebar for you to use in your search for what you need.','k2_domain'); ?></p>
		</div>

	</div> <!-- .hentry .four04 -->

<?php endif; /* End Loop Init  */ ?>

<?php /* Bottom Navigation */ if ( ('0' == $k2rollingarchives) or is_single() ): k2_navigation('nav-below'); endif; ?> 

<?php if ( isset( $_GET['k2dynamic'] ) ): ?>
</div><!-- #dynamictype -->
<?php endif; ?>

Paragamer, that sounds like a fantastic idea. I will definitely give that a shot, too! Thank you!