// Add backend styles for Gutenberg.
add_action( 'enqueue_block_editor_assets', 'add_gutenberg_assets' );

/**
 * Load Gutenberg stylesheet.
 */
function add_gutenberg_assets() {
    // Load the theme styles within Gutenberg.
    wp_enqueue_style( 'photographus-gutenberg', get_theme_file_uri( '/dist/gutenberg-editor-style.css' ), false );
}