Add a widget area to the bottom of single posts (Genesis - XHTML - functions.php)

Add a widget area to the bottom of single posts

// Add the newsletter widget after the post content
add_action( 'genesis_after_post_content', 'nabm_add_newsletter_box' );
function nabm_add_newsletter_box() {
	if ( is_singular( 'post' ) )
	genesis_widget_area( 'newsletter', array(
		'before' => '<div id="newsletter">',
	) );
}

genesis_register_sidebar( array(
	'id'		=> 'newsletter',
	'name'		=> __( 'Newsletter', 'nabm' ),
	'description'	=> __( 'This is the newsletter section.', 'nabm' ),
) );

Sample CSS for Newsletter Widget

/* Newsletter
------------------------------------------------------------ */

#newsletter {
	background-color: #e2e2e2 !important;
	color: #333;
	line-height: 1.5;
	padding: 20px;
	padding: 2rem;
        margin-top: 30px !important;
}
 
#newsletter p {
	margin-bottom: 15px;
	margin-bottom: 1.5rem;
}

#newsletter h4 {
        color: #017172;
        text-align: center;
}
 
#newsletter input {
	width: 50%;
}