Changing header banner dimension in child theme

Question

I'm using Twenty Thirteen Child theme for my website running WP 4.5.3. I would like to change the header banner dimension to 900x480.

The content of my twentythirteen-child/functions.php:

<?php
add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );
function theme_enqueue_styles() {
    wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );

}


// remove default action from Twenty Twelve
/*remove_action( 'after_setup_theme', 'twentythirteen_custom_header_setup' );*/

function twentythirteenchild_custom_header_setup() {
    $args = array(
        // Text color and image (empty to use none).
        'default-text-color'     => '220e10',
        'default-image'          => '%s/images/headers/circle.png',

        // Set height and width, with a maximum value for the width.
        'height'                 => 480,
        'width'                  => 900,

        // Callbacks for styling the header and the admin preview.
        'wp-head-callback'       => 'twentythirteen_header_style',
        'admin-head-callback'    => 'twentythirteen_admin_header_style',
        'admin-preview-callback' => 'twentythirteen_admin_header_image',
    );

    add_theme_support( 'custom-header', $args );

}
add_action( 'after_setup_theme', 'twentythirteenchild_custom_header_setup', 11 );

remove_filter( 'HEADER_IMAGE_WIDTH', 'twentyeleven_header_image_width' );
remove_filter( 'HEADER_IMAGE_HEIGHT', 'twentyeleven_header_image_height' );
define( 'HEADER_IMAGE_WIDTH', apply_filters( 'twentythirteen_header_image_width', 900 ) );
define( 'HEADER_IMAGE_HEIGHT', apply_filters( 'twentythirteen_header_image_height', 480 ) );

It works, but only partially.

When adding a 900x480 image, I obtained:

which is good. When either pressing on Crop Image or Skip Cropping, I obtained:

which is not good at all.

Could you please help?

Thank you very much in advance!!

Answer 1

Problem solved.

.site-header {
    background: url(<?php header_image(); ?>) no-repeat scroll top;
    background-size: 900px auto!important;
}