wordpress – site not update after update style.css

This most likely is a caching issue on the server side. Check in your functions.php if the stylesheet is enqueued using the version number. Failing to do so is the most common reason WordPress caching plugins ignore updates to style.css. It should look a bit like this:

    $theme_data = wp_get_theme();
    wp_enqueue_style('main-style', get_template_directory_uri() . '/style.css', '', $theme_data['version'], 'all');

Otherwise, it might be that the webserver software is caching agressively. In that case waiting a few hours may be your only recourse.