why wp_enqueue_scripts() not working?

Hey bro Use this code get_stylesheet_directory_uri

function custom_theme_script(){
    wp_register_style('bootstrap', get_stylesheet_directory_uri.() .'/css/bootstrap.css' );

    wp_enqueue_style('bootstrap');

    wp_register_style('style', get_stylesheet_directory_uri() . '/css/style.css');

    wp_enqueue_style('style');

       wp_deregister_script( 'jquery' );
    wp_enqueue_script('bootstrap.min', get_template_directory_uri() . '/js/bootstrap.min.js', array(), '3.5.1', true );
}

add_action('wp_enqueue_scripts', 'custom_theme_script');

`