New smaller featured image size to fit layout. RICG for featured images.

functions.php

@@ -41,7 +41,7 @@ function kuhn_setup() {
 	 * @link https://developer.wordpress.org/themes/functionality/featured-images-post-thumbnails/
 	 */
 	add_theme_support( 'post-thumbnails' );
-	add_image_size( 'kuhn-index', 1045, 600, true);
+	add_image_size( 'kuhn-index', 966, 555, true);
 
 	// This theme uses wp_nav_menu() in one location.
 	register_nav_menus( array(
@@ -161,31 +161,15 @@ function kuhn_resource_hints( $urls, $relation_type ) {
 function kuhn_content_image_sizes_attr( $sizes, $size ) {
 	if ( is_singular() ) {
 		$width = $size[0];
-		if ( 720 <= $width ) {
+		if ( 610 <= $width ) {
 			$sizes = '(min-width: 990px) 720px, (min-width: 1300px) 610px, 95vw';
 		}
 		return $sizes;
 	}
 }
 add_filter( 'wp_calculate_image_sizes', 'kuhn_content_image_sizes_attr', 10, 2 );
 
-/**
- * Filter the `sizes` value in the header image markup.
- *
- * @origin Twenty Seventeen 1.0
- *
- * @param string $html   The HTML image tag markup being filtered.
- * @param object $header The custom header object returned by 'get_custom_header()'.
- * @param array  $attr   Array of the attributes for the image tag.
- * @return string The filtered header image HTML.
- */
-function kuhn_header_image_tag( $html, $header, $attr ) {
-	if ( isset( $attr['sizes'] ) ) {
-		$html = str_replace( $attr['sizes'], '100vw', $html );
-	}
-	return $html;
-}
-add_filter( 'get_header_image_tag', 'kuhn_header_image_tag', 10, 3 );
+
 /**
  * Add custom image sizes attribute to enhance responsive image functionality
  * for post thumbnails.
@@ -198,17 +182,16 @@ function kuhn_header_image_tag( $html, $header, $attr ) {
  * @return string A source size value for use in a post thumbnail 'sizes' attribute.
  */
 function kuhn_post_thumbnail_sizes_attr( $attr, $attachment, $size ) {
-	if ( !is_singular() ) {
-		if ( is_active_sidebar( 'sidebar-1' ) ) {
-			$attr['sizes'] = '(max-width: 900px) 90vw, 800px';
-		} else {
-			$attr['sizes'] = '(max-width: 1000px) 90vw, 1000px';
-		}
+	if ( is_singular() ) {
+		$attr['sizes'] = '(min-width: 990px) 720px, (min-width: 1300px) 820px, 95vw';
+	} else {
+		$attr['sizes'] = '(min-width: 990px) 955px, (min-width: 1300px) 966px, 95vw';
 	}
 	return $attr;
 }
 add_filter( 'wp_get_attachment_image_attributes', 'kuhn_post_thumbnail_sizes_attr', 10, 3 );
 
+
 /**
  * Register widget area.
  *