Add image to top of pages and posts

functions.php

add_image_size( 'featured-top', 750, 500, TRUE );

add_action ('genesis_before_loop','add_top_image');
function add_top_image(){
	if (is_page() || is_single()){
		the_post_thumbnail('featured-top',array('class'=>'top-of-post'));
	}
}

// Use this one if it's full width and needs to be a background image
 add_action('genesis_after_header','add_top_img',12);
 function add_top_img(){
	 if (is_page()){
		echo '<div class="top-image" style="background-image:url(';
         the_post_thumbnail_url();
         echo ')"></div>';
	 }
 }

style.css

.top-image {
    width: 100%;
    height: 255px;
    background-size: cover;
    background-position: center;
}
	
@media screen and (max-width:1023px){
  /* This includes 768px*/	
  .top-image {
    height: 200px;
	}
}

change 750 and 500 to correct dimensions