Rewriting in wordpress url

From this other answer on the WP SE

add_action('generate_rewrite_rules', 'roots_add_rewrites');

function roots_add_rewrites($content) {
    $theme_name = next(explode('/themes/', get_stylesheet_directory()));
    global $wp_rewrite;
    $roots_new_non_wp_rules = array(
        'css/(.*)'      => 'wp-content/themes/'. $theme_name . '/css/$1',
        'js/(.*)'       => 'wp-content/themes/'. $theme_name . '/js/$1',
        'img/(.*)'      => 'wp-content/themes/'. $theme_name . '/img/$1',
    );
    $wp_rewrite->non_wp_rules += $roots_new_non_wp_rules;
}

TheDeadMedic provided a much better version of this function:

function wpse_208051_add_rewrites( $wp_rewrite ) {
    $path = str_replace( home_url( "https://wordpress.stackexchange.com/" ), '', get_template_directory_uri() );

    $wp_rewrite->non_wp_rules += array(
        'css/(.*)' => $path . '/css/$1',
        'js/(.*)'  => $path . '/js/$1',
        'img/(.*)' => $path . '/img/$1',
    );
}

add_action( 'generate_rewrite_rules', 'wpse_208051_add_rewrites' );