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/* Add these styles to Modern Portfolio Pro for the category Design template */
/* Category Design Entries
--------------------------------------------- */

/* Adds the opacity and hover feature to images */
.category-design img {
	margin-bottom: 16px;
	margin-bottom: 1.6rem;
	opacity: 0.8;
}

.category-design  img:hover {
	opacity: 1;
}

/*  Adds the grid column width the same as the home page */
.category-design .entry {
	float: left;
	margin-right: 5.263157894737%; /* 60px / 1140px */
	width: 29.824561403509%; /* 340px / 1140px */
}

/* Removes the right margin on the 3rd, 6th, 9th, etc. posts */
.category-design .entry:nth-of-type(3n+3) {
	margin-right: 0;
}

/* Clears the float to start a new row for the 4th, 7th, etc. posts */
.category-design .entry:nth-of-type(3n+1) {
	clear: left;
}

/* Smaller title size */
.category-design .entry-title {
	font-size: 18px;
}

@media only screen and (max-width: 600px) {
  /* Category Design Entries 
	--------------------------------------- */
	
	/* Centers the posts or entries */
	.category-design .entry {
		text-align: center;
	}
	
	/* Removes the three across grid */
	.category-design .entry,
	.category-design .entry:nth-of-type(3n+3) {
		float: none;
		margin: 0 auto 24px;
		margin: 0 auto 2.4rem;
		max-width: 340px;
		width: 100%;
	}
  
}

<?php //Remove this and add only what's below

// Change posts per page in the design category
add_action( 'pre_get_posts', 'mp_design_cat_posts_per_page' );
function mp_design_cat_posts_per_page( $query ) {
	if( $query->is_main_query() && is_category( 'design' ) && ! is_admin() ) {
		$query->set( 'posts_per_page', '12' );
	}
}

<?php
/**
 * The custom template for the Design category for Modern Portfolio Pro
 */

//* Force full width content layout
add_filter( 'genesis_pre_get_option_site_layout', '__genesis_return_full_width_content' );

//* Remove the entry meta in the entry header
remove_action( 'genesis_entry_header', 'genesis_entry_header_markup_open', 5 );
remove_action( 'genesis_entry_header', 'genesis_post_info', 12 );
remove_action( 'genesis_entry_header', 'genesis_entry_header_markup_close', 15 );

//* Remove the entry content
remove_action( 'genesis_entry_content', 'genesis_do_post_content' );

//* Remove the entry image
remove_action( 'genesis_entry_content', 'genesis_do_post_image', 8 );

//* Add the featured image before post title
add_action( 'genesis_entry_header', 'minimum_portfolio_grid', 8 );
function minimum_portfolio_grid() {

	if ( $image = genesis_get_image( 'format=url&size=portfolio' ) ) {
		printf( '<div class="portfolio-image"><a href="%s" rel="bookmark"><img src="%s" alt="%s" /></a></div>', get_permalink(), $image, the_title_attribute( 'echo=0' ) );
	}
}

//* Remove the entry meta in the entry footer
remove_action( 'genesis_entry_footer', 'genesis_entry_footer_markup_open', 5 );
remove_action( 'genesis_entry_footer', 'genesis_post_meta' );
remove_action( 'genesis_entry_footer', 'genesis_entry_footer_markup_close', 15 );

//* Run the Genesis loop
genesis();