Custom CSS does not work with SSL

When I use this plugin with a custom CSS file for the form, the plugin will attempt to load the CSS file from a non-SSL (http) address even if I access the page using SSL (https). Chrome will not load that CSS.

This problem can be solved with a slight modification to user-submitted-posts.php on line 252:

Current:
$base_url = WP_PLUGIN_URL .'/'. basename(dirname(__FILE__));
Better:
$base_url = plugins_url() .'/'. basename(dirname(__FILE__));

https://ww.wp.xz.cn/plugins/user-submitted-posts/