FM / includes

/var/www/p4ela.net/www/wp-admin/includes/

/var/www/p4ela.net/www/wp-admin/includes

Name	Size	Mode	Actions
admin-filters.php	8082	0666	edit dl rm
admin.php	3628	0666	edit dl rm
ajax-actions.php	151627	0666	edit dl rm
bookmark.php	11615	0666	edit dl rm
class-automatic-upgrader-skin.php	3663	0666	edit dl rm
class-bulk-plugin-upgrader-skin.php	2590	0666	edit dl rm
class-bulk-theme-upgrader-skin.php	2660	0666	edit dl rm
class-bulk-upgrader-skin.php	6753	0666	edit dl rm
class-core-upgrader.php	15191	0666	edit dl rm
class-custom-background.php	21619	0666	edit dl rm
class-custom-image-header.php	49064	0666	edit dl rm
class-file-upload-upgrader.php	4163	0666	edit dl rm
class-ftp-pure.php	5426	0666	edit dl rm
class-ftp-sockets.php	8479	0666	edit dl rm
class-ftp.php	27304	0666	edit dl rm
class-language-pack-upgrader-skin.php	2870	0666	edit dl rm
class-language-pack-upgrader.php	15561	0666	edit dl rm
class-pclzip.php	196700	0666	edit dl rm
class-plugin-installer-skin.php	12053	0666	edit dl rm
class-plugin-upgrader-skin.php	3278	0666	edit dl rm
class-plugin-upgrader.php	23243	0666	edit dl rm
class-theme-installer-skin.php	12734	0666	edit dl rm
class-theme-upgrader-skin.php	4176	0666	edit dl rm
class-theme-upgrader.php	26702	0666	edit dl rm
class-walker-category-checklist.php	5091	0666	edit dl rm
class-walker-nav-menu-checklist.php	5708	0666	edit dl rm
class-walker-nav-menu-edit.php	14265	0666	edit dl rm
class-wp-ajax-upgrader-skin.php	4193	0666	edit dl rm
class-wp-application-passwords-list-table.php	6949	0666	edit dl rm
class-wp-automatic-updater.php	61136	0666	edit dl rm
class-wp-comments-list-table.php	32918	0666	edit dl rm
class-wp-community-events.php	18769	0666	edit dl rm
class-wp-debug-data.php	65288	0666	edit dl rm
class-wp-filesystem-base.php	24410	0666	edit dl rm
class-wp-filesystem-direct.php	18143	0666	edit dl rm
class-wp-filesystem-ftpext.php	23101	0666	edit dl rm
class-wp-filesystem-ftpsockets.php	18479	0666	edit dl rm
class-wp-filesystem-ssh2.php	23310	0666	edit dl rm
class-wp-importer.php	7465	0666	edit dl rm
class-wp-internal-pointers.php	4577	0666	edit dl rm
class-wp-links-list-table.php	9241	0666	edit dl rm
class-wp-list-table-compat.php	1497	0666	edit dl rm
class-wp-list-table.php	52864	0666	edit dl rm
class-wp-media-list-table.php	25629	0666	edit dl rm
class-wp-ms-sites-list-table.php	22026	0666	edit dl rm
class-wp-ms-themes-list-table.php	28334	0666	edit dl rm
class-wp-ms-users-list-table.php	15287	0666	edit dl rm
class-wp-plugin-install-list-table.php	24786	0666	edit dl rm
class-wp-plugins-list-table.php	57786	0666	edit dl rm
class-wp-post-comments-list-table.php	1453	0666	edit dl rm
class-wp-posts-list-table.php	63946	0666	edit dl rm
class-wp-privacy-data-export-requests-list-table.php	5563	0666	edit dl rm
class-wp-privacy-data-removal-requests-list-table.php	5715	0666	edit dl rm
class-wp-privacy-policy-content.php	32777	0666	edit dl rm
class-wp-privacy-requests-table.php	13974	0666	edit dl rm
class-wp-screen.php	37327	0666	edit dl rm
class-wp-site-health-auto-updates.php	13561	0666	edit dl rm
class-wp-site-health.php	122364	0666	edit dl rm
class-wp-site-icon.php	6414	0666	edit dl rm
class-wp-terms-list-table.php	21182	0666	edit dl rm
class-wp-theme-install-list-table.php	15792	0666	edit dl rm
class-wp-themes-list-table.php	10344	0666	edit dl rm
class-wp-upgrader-skin.php	7110	0666	edit dl rm
class-wp-upgrader-skins.php	1477	0666	edit dl rm
class-wp-upgrader.php	47695	0666	edit dl rm
class-wp-users-list-table.php	19058	0666	edit dl rm
comment.php	6121	0666	edit dl rm
continents-cities.php	20540	0666	edit dl rm
credits.php	5864	0666	edit dl rm
dashboard.php	69710	0666	edit dl rm
deprecated.php	41776	0666	edit dl rm
edit-tag-messages.php	1478	0666	edit dl rm
export.php	25565	0666	edit dl rm
file.php	97575	0666	edit dl rm
image-edit.php	43850	0666	edit dl rm
image.php	43422	0666	edit dl rm
import.php	6617	0666	edit dl rm
list-table.php	3802	0666	edit dl rm
media.php	118870	0666	edit dl rm
menu.php	9618	0666	edit dl rm
meta-boxes.php	66084	0666	edit dl rm
misc.php	46465	0666	edit dl rm
ms-admin-filters.php	1296	0666	edit dl rm
ms-deprecated.php	3770	0666	edit dl rm
ms.php	33958	0666	edit dl rm
nav-menu.php	48905	0666	edit dl rm
network.php	26980	0666	edit dl rm
noop.php	1148	0666	edit dl rm
options.php	4251	0666	edit dl rm
plugin-install.php	39474	0666	edit dl rm
plugin.php	92925	0666	edit dl rm
post.php	81683	0666	edit dl rm
privacy-tools.php	33462	0666	edit dl rm
revision.php	16496	0666	edit dl rm
schema.php	42659	0666	edit dl rm
screen.php	6378	0666	edit dl rm
taxonomy.php	8424	0666	edit dl rm
template.php	98626	0666	edit dl rm
theme-install.php	6990	0666	edit dl rm
theme.php	47742	0666	edit dl rm
translation-install.php	11075	0666	edit dl rm
update-core.php	69331	0666	edit dl rm
update.php	34429	0666	edit dl rm
upgrade.php	113892	0666	edit dl rm
user.php	23740	0666	edit dl rm
widgets.php	10912	0666	edit dl rm

Edit: /var/www/p4ela.net/www/wp-admin/includes/class-custom-background.php (21619B)

<?php
/**
 * The custom background script.
 *
 * @package WordPress
 * @subpackage Administration
 */

/**
 * The custom background class.
 *
 * @since 3.0.0
 */
#[AllowDynamicProperties]
class Custom_Background {

/**
	 * Callback for administration header.
	 *
	 * @since 3.0.0
	 * @var callable
	 */
	public $admin_header_callback;

/**
	 * Callback for header div.
	 *
	 * @since 3.0.0
	 * @var callable
	 */
	public $admin_image_div_callback;

/**
	 * Used to trigger a success message when settings updated and set to true.
	 *
	 * @since 3.0.0
	 * @var bool
	 */
	private $updated;

/**
	 * Constructor - Registers administration header callback.
	 *
	 * @since 3.0.0
	 *
	 * @param callable $admin_header_callback    Optional. Administration header callback.
	 *                                           Default empty string.
	 * @param callable $admin_image_div_callback Optional. Custom image div output callback.
	 *                                           Default empty string.
	 */
	public function __construct( $admin_header_callback = '', $admin_image_div_callback = '' ) {
		$this->admin_header_callback    = $admin_header_callback;
		$this->admin_image_div_callback = $admin_image_div_callback;

add_action( 'admin_menu', array( $this, 'init' ) );

add_action( 'wp_ajax_custom-background-add', array( $this, 'ajax_background_add' ) );

// Unused since 3.5.0.
		add_action( 'wp_ajax_set-background-image', array( $this, 'wp_set_background_image' ) );
	}

/**
	 * Sets up the hooks for the Custom Background admin page.
	 *
	 * @since 3.0.0
	 */
	public function init() {
		$page = add_theme_page(
			_x( 'Background', 'custom background' ),
			_x( 'Background', 'custom background' ),
			'edit_theme_options',
			'custom-background',
			array( $this, 'admin_page' )
		);

if ( ! $page ) {
			return;
		}

add_action( "load-{$page}", array( $this, 'admin_load' ) );
		add_action( "load-{$page}", array( $this, 'take_action' ), 49 );
		add_action( "load-{$page}", array( $this, 'handle_upload' ), 49 );

if ( $this->admin_header_callback ) {
			add_action( "admin_head-{$page}", $this->admin_header_callback, 51 );
		}
	}

/**
	 * Sets up the enqueue for the CSS & JavaScript files.
	 *
	 * @since 3.0.0
	 */
	public function admin_load() {
		get_current_screen()->add_help_tab(
			array(
				'id'      => 'overview',
				'title'   => __( 'Overview' ),
				'content' =>
					'<p>' . __( 'You can customize the look of your site without touching any of your theme&#8217;s code by using a custom background. Your background can be an image or a color.' ) . '</p>' .
					'<p>' . __( 'To use a background image, simply upload it or choose an image that has already been uploaded to your Media Library by clicking the &#8220;Choose Image&#8221; button. You can display a single instance of your image, or tile it to fill the screen. You can have your background fixed in place, so your site content moves on top of it, or you can have it scroll with your site.' ) . '</p>' .
					'<p>' . __( 'You can also choose a background color by clicking the Select Color button and either typing in a legitimate HTML hex value, e.g. &#8220;#ff0000&#8221; for red, or by choosing a color using the color picker.' ) . '</p>' .
					'<p>' . __( 'Do not forget to click on the Save Changes button when you are finished.' ) . '</p>',
			)
		);

get_current_screen()->set_help_sidebar(
			'<p><strong>' . __( 'For more information:' ) . '</strong></p>' .
			'<p>' . __( '<a href="https://codex.wordpress.org/Appearance_Background_Screen">Documentation on Custom Background</a>' ) . '</p>' .
			'<p>' . __( '<a href="https://wordpress.org/support/forums/">Support forums</a>' ) . '</p>'
		);

wp_enqueue_media();
		wp_enqueue_script( 'custom-background' );
		wp_enqueue_style( 'wp-color-picker' );
	}

/**
	 * Executes custom background modification.
	 *
	 * @since 3.0.0
	 */
	public function take_action() {
		if ( empty( $_POST ) ) {
			return;
		}

if ( isset( $_POST['reset-background'] ) ) {
			check_admin_referer( 'custom-background-reset', '_wpnonce-custom-background-reset' );

remove_theme_mod( 'background_image' );
			remove_theme_mod( 'background_image_thumb' );

$this->updated = true;
			return;
		}

if ( isset( $_POST['remove-background'] ) ) {
			// @todo Uploaded files are not removed here.
			check_admin_referer( 'custom-background-remove', '_wpnonce-custom-background-remove' );

set_theme_mod( 'background_image', '' );
			set_theme_mod( 'background_image_thumb', '' );

$this->updated = true;
			wp_safe_redirect( $_POST['_wp_http_referer'] );
			return;
		}

if ( isset( $_POST['background-preset'] ) ) {
			check_admin_referer( 'custom-background' );

if ( in_array( $_POST['background-preset'], array( 'default', 'fill', 'fit', 'repeat', 'custom' ), true ) ) {
				$preset = $_POST['background-preset'];
			} else {
				$preset = 'default';
			}

set_theme_mod( 'background_preset', $preset );
		}

if ( isset( $_POST['background-position'] ) ) {
			check_admin_referer( 'custom-background' );

$position = explode( ' ', $_POST['background-position'] );

if ( in_array( $position[0], array( 'left', 'center', 'right' ), true ) ) {
				$position_x = $position[0];
			} else {
				$position_x = 'left';
			}

if ( in_array( $position[1], array( 'top', 'center', 'bottom' ), true ) ) {
				$position_y = $position[1];
			} else {
				$position_y = 'top';
			}

set_theme_mod( 'background_position_x', $position_x );
			set_theme_mod( 'background_position_y', $position_y );
		}

if ( isset( $_POST['background-size'] ) ) {
			check_admin_referer( 'custom-background' );

if ( in_array( $_POST['background-size'], array( 'auto', 'contain', 'cover' ), true ) ) {
				$size = $_POST['background-size'];
			} else {
				$size = 'auto';
			}

set_theme_mod( 'background_size', $size );
		}

if ( isset( $_POST['background-repeat'] ) ) {
			check_admin_referer( 'custom-background' );

$repeat = $_POST['background-repeat'];

if ( 'no-repeat' !== $repeat ) {
				$repeat = 'repeat';
			}

set_theme_mod( 'background_repeat', $repeat );
		}

if ( isset( $_POST['background-attachment'] ) ) {
			check_admin_referer( 'custom-background' );

$attachment = $_POST['background-attachment'];

if ( 'fixed' !== $attachment ) {
				$attachment = 'scroll';
			}

set_theme_mod( 'background_attachment', $attachment );
		}

if ( isset( $_POST['background-color'] ) ) {
			check_admin_referer( 'custom-background' );

$color = preg_replace( '/[^0-9a-fA-F]/', '', $_POST['background-color'] );

if ( strlen( $color ) === 6 || strlen( $color ) === 3 ) {
				set_theme_mod( 'background_color', $color );
			} else {
				set_theme_mod( 'background_color', '' );
			}
		}

$this->updated = true;
	}

/**
	 * Displays the custom background page.
	 *
	 * @since 3.0.0
	 */
	public function admin_page() {
		?>
<div class="wrap" id="custom-background">
<h1><?php _e( 'Custom Background' ); ?></h1>

<?php
		if ( current_user_can( 'customize' ) ) {
			$message = sprintf(
				/* translators: %s: URL to background image configuration in Customizer. */
				__( 'You can now manage and live-preview Custom Backgrounds in the <a href="%s">Customizer</a>.' ),
				admin_url( 'customize.php?autofocus[control]=background_image' )
			);
			wp_admin_notice(
				$message,
				array(
					'type'               => 'info',
					'additional_classes' => array( 'hide-if-no-customize' ),
				)
			);
		}

if ( ! empty( $this->updated ) ) {
			$updated_message = sprintf(
				/* translators: %s: Home URL. */
				__( 'Background updated. <a href="%s">Visit your site</a> to see how it looks.' ),
				esc_url( home_url( '/' ) )
			);
			wp_admin_notice(
				$updated_message,
				array(
					'id'                 => 'message',
					'additional_classes' => array( 'updated' ),
				)
			);
		}
		?>

<table class="form-table" role="presentation">
<tbody>
<tr>
<th scope="row"><?php _e( 'Preview' ); ?></th>
<td>
		<?php
		if ( $this->admin_image_div_callback ) {
			call_user_func( $this->admin_image_div_callback );
		} else {
			$background_styles = '';
			$bgcolor           = get_background_color();
			if ( $bgcolor ) {
				$background_styles .= 'background-color: #' . $bgcolor . ';';
			}

$background_image_thumb = get_background_image();
			if ( $background_image_thumb ) {
				$background_image_thumb = esc_url( set_url_scheme( get_theme_mod( 'background_image_thumb', str_replace( '%', '%%', $background_image_thumb ) ) ) );
				$background_position_x  = get_theme_mod( 'background_position_x', get_theme_support( 'custom-background', 'default-position-x' ) );
				$background_position_y  = get_theme_mod( 'background_position_y', get_theme_support( 'custom-background', 'default-position-y' ) );
				$background_size        = get_theme_mod( 'background_size', get_theme_support( 'custom-background', 'default-size' ) );
				$background_repeat      = get_theme_mod( 'background_repeat', get_theme_support( 'custom-background', 'default-repeat' ) );
				$background_attachment  = get_theme_mod( 'background_attachment', get_theme_support( 'custom-background', 'default-attachment' ) );

// Background-image URL must be single quote, see below.
				$background_styles .= " background-image: url('$background_image_thumb');"
				. " background-size: $background_size;"
				. " background-position: $background_position_x $background_position_y;"
				. " background-repeat: $background_repeat;"
				. " background-attachment: $background_attachment;";
			}
			?>
	<div id="custom-background-image" style="<?php echo $background_styles; ?>"><?php // Must be double quote, see above. ?>
			<?php if ( $background_image_thumb ) { ?>
		<img class="custom-background-image" src="<?php echo $background_image_thumb; ?>" style="visibility:hidden;" alt="" /><br />
		<img class="custom-background-image" src="<?php echo $background_image_thumb; ?>" style="visibility:hidden;" alt="" />
		<?php } ?>
	</div>
	<?php } ?>
</td>
</tr>

<?php if ( get_background_image() ) : ?>
<tr>
<th scope="row"><?php _e( 'Remove Image' ); ?></th>
<td>
<form method="post">
			<?php wp_nonce_field( 'custom-background-remove', '_wpnonce-custom-background-remove' ); ?>
			<?php submit_button( __( 'Remove Background Image' ), '', 'remove-background', false ); ?><br />
			<?php _e( 'This will remove the background image. You will not be able to restore any customizations.' ); ?>
</form>
</td>
</tr>
		<?php endif; ?>

<?php $default_image = get_theme_support( 'custom-background', 'default-image' ); ?>
		<?php if ( $default_image && get_background_image() !== $default_image ) : ?>
<tr>
<th scope="row"><?php _e( 'Restore Original Image' ); ?></th>
<td>
<form method="post">
			<?php wp_nonce_field( 'custom-background-reset', '_wpnonce-custom-background-reset' ); ?>
			<?php submit_button( __( 'Restore Original Image' ), '', 'reset-background', false ); ?><br />
			<?php _e( 'This will restore the original background image. You will not be able to restore any customizations.' ); ?>
</form>
</td>
</tr>
		<?php endif; ?>

<?php if ( current_user_can( 'upload_files' ) ) : ?>
<tr>
<th scope="row"><?php _e( 'Select Image' ); ?></th>
<td><form enctype="multipart/form-data" id="upload-form" class="wp-upload-form" method="post">
	<p>
		<label for="upload"><?php _e( 'Choose an image from your computer:' ); ?></label><br />
		<input type="file" id="upload" name="import" />
		<input type="hidden" name="action" value="save" />
			<?php wp_nonce_field( 'custom-background-upload', '_wpnonce-custom-background-upload' ); ?>
			<?php submit_button( __( 'Upload' ), '', 'submit', false ); ?>
	</p>
	<p>
		<label for="choose-from-library-link"><?php _e( 'Or choose an image from your media library:' ); ?></label><br />
		<button id="choose-from-library-link" class="button"
			data-choose="<?php esc_attr_e( 'Choose a Background Image' ); ?>"
			data-update="<?php esc_attr_e( 'Set as background' ); ?>"><?php _e( 'Choose Image' ); ?></button>
	</p>
	</form>
</td>
</tr>
		<?php endif; ?>
</tbody>
</table>

<?php
			$background_position = sprintf(
				'%s %s',
				get_theme_mod( 'background_position_x', get_theme_support( 'custom-background', 'default-position-x' ) ),
				get_theme_mod( 'background_position_y', get_theme_support( 'custom-background', 'default-position-y' ) )
			);

$background_position_options = array(
				array(
					'left top'   => array(
						'label' => __( 'Top Left' ),
						'icon'  => 'dashicons dashicons-arrow-left-alt',
					),
					'center top' => array(
						'label' => __( 'Top' ),
						'icon'  => 'dashicons dashicons-arrow-up-alt',
					),
					'right top'  => array(
						'label' => __( 'Top Right' ),
						'icon'  => 'dashicons dashicons-arrow-right-alt',
					),
				),
				array(
					'left center'   => array(
						'label' => __( 'Left' ),
						'icon'  => 'dashicons dashicons-arrow-left-alt',
					),
					'center center' => array(
						'label' => __( 'Center' ),
						'icon'  => 'background-position-center-icon',
					),
					'right center'  => array(
						'label' => __( 'Right' ),
						'icon'  => 'dashicons dashicons-arrow-right-alt',
					),
				),
				array(
					'left bottom'   => array(
						'label' => __( 'Bottom Left' ),
						'icon'  => 'dashicons dashicons-arrow-left-alt',
					),
					'center bottom' => array(
						'label' => __( 'Bottom' ),
						'icon'  => 'dashicons dashicons-arrow-down-alt',
					),
					'right bottom'  => array(
						'label' => __( 'Bottom Right' ),
						'icon'  => 'dashicons dashicons-arrow-right-alt',
					),
				),
			);
			?>
<tr>
<th scope="row"><?php _e( 'Image Position' ); ?></th>
<td><fieldset><legend class="screen-reader-text"><span>
			<?php
			/* translators: Hidden accessibility text. */
			_e( 'Image Position' );
			?>
</span></legend>
<div class="background-position-control">
			<?php foreach ( $background_position_options as $group ) : ?>
	<div class="button-group">
				<?php foreach ( $group as $value => $input ) : ?>
		<label>
			<input class="ui-helper-hidden-accessible" name="background-position" type="radio" value="<?php echo esc_attr( $value ); ?>"<?php checked( $value, $background_position ); ?>>
			<span class="button display-options position"><span class="<?php echo esc_attr( $input['icon'] ); ?>" aria-hidden="true"></span></span>
			<span class="screen-reader-text"><?php echo $input['label']; ?></span>
		</label>
	<?php endforeach; ?>
	</div>
<?php endforeach; ?>
</div>
</fieldset></td>
</tr>

<?php wp_nonce_field( 'custom-background' ); ?>
		<?php submit_button( null, 'primary', 'save-background-options' ); ?>
</form>

</div>
		<?php
	}

/**
	 * Handles an Image upload for the background image.
	 *
	 * @since 3.0.0
	 */
	public function handle_upload() {
		if ( empty( $_FILES ) ) {
			return;
		}

check_admin_referer( 'custom-background-upload', '_wpnonce-custom-background-upload' );

$overrides = array( 'test_form' => false );

$uploaded_file = $_FILES['import'];
		$wp_filetype   = wp_check_filetype_and_ext( $uploaded_file['tmp_name'], $uploaded_file['name'] );
		if ( ! wp_match_mime_types( 'image', $wp_filetype['type'] ) ) {
			wp_die( __( 'The uploaded file is not a valid image. Please try again.' ) );
		}

$file = wp_handle_upload( $uploaded_file, $overrides );

if ( isset( $file['error'] ) ) {
			wp_die( $file['error'] );
		}

$url      = $file['url'];
		$type     = $file['type'];
		$file     = $file['file'];
		$filename = wp_basename( $file );

// Construct the attachment array.
		$attachment = array(
			'post_title'     => $filename,
			'post_content'   => $url,
			'post_mime_type' => $type,
			'guid'           => $url,
			'context'        => 'custom-background',
		);

// Save the data.
		$id = wp_insert_attachment( $attachment, $file );

// Add the metadata.
		wp_update_attachment_metadata( $id, wp_generate_attachment_metadata( $id, $file ) );
		update_post_meta( $id, '_wp_attachment_is_custom_background', get_option( 'stylesheet' ) );

set_theme_mod( 'background_image', sanitize_url( $url ) );

$thumbnail = wp_get_attachment_image_src( $id, 'thumbnail' );
		set_theme_mod( 'background_image_thumb', sanitize_url( $thumbnail[0] ) );

/** This filter is documented in wp-admin/includes/class-custom-image-header.php */
		$file = apply_filters( 'wp_create_file_in_uploads', $file, $id ); // For replication.

$this->updated = true;
	}

/**
	 * Handles Ajax request for adding custom background context to an attachment.
	 *
	 * Triggers when the user adds a new background image from the
	 * Media Manager.
	 *
	 * @since 4.1.0
	 */
	public function ajax_background_add() {
		check_ajax_referer( 'background-add', 'nonce' );

if ( ! current_user_can( 'edit_theme_options' ) ) {
			wp_send_json_error();
		}

$attachment_id = absint( $_POST['attachment_id'] );
		if ( $attachment_id < 1 ) {
			wp_send_json_error();
		}

update_post_meta( $attachment_id, '_wp_attachment_is_custom_background', get_stylesheet() );

wp_send_json_success();
	}

/**
	 * @since 3.4.0
	 * @deprecated 3.5.0
	 *
	 * @param array $form_fields
	 * @return array $form_fields
	 */
	public function attachment_fields_to_edit( $form_fields ) {
		return $form_fields;
	}

/**
	 * @since 3.4.0
	 * @deprecated 3.5.0
	 *
	 * @param array $tabs
	 * @return array $tabs
	 */
	public function filter_upload_tabs( $tabs ) {
		return $tabs;
	}

/**
	 * @since 3.4.0
	 * @deprecated 3.5.0
	 */
	public function wp_set_background_image() {
		check_ajax_referer( 'custom-background' );

if ( ! current_user_can( 'edit_theme_options' ) || ! isset( $_POST['attachment_id'] ) ) {
			exit;
		}

$attachment_id = absint( $_POST['attachment_id'] );

$sizes = array_keys(
			/** This filter is documented in wp-admin/includes/media.php */
			apply_filters(
				'image_size_names_choose',
				array(
					'thumbnail' => __( 'Thumbnail' ),
					'medium'    => __( 'Medium' ),
					'large'     => __( 'Large' ),
					'full'      => __( 'Full Size' ),
				)
			)
		);

$size = 'thumbnail';
		if ( in_array( $_POST['size'], $sizes, true ) ) {
			$size = esc_attr( $_POST['size'] );
		}

update_post_meta( $attachment_id, '_wp_attachment_is_custom_background', get_option( 'stylesheet' ) );

$url       = wp_get_attachment_image_src( $attachment_id, $size );
		$thumbnail = wp_get_attachment_image_src( $attachment_id, 'thumbnail' );
		set_theme_mod( 'background_image', sanitize_url( $url[0] ) );
		set_theme_mod( 'background_image_thumb', sanitize_url( $thumbnail[0] ) );
		exit;
	}
}

cmd: