There are three reasons that I know about that can cause this.
First, when something is incorrectly written in config.phpline 17 $config['base_url'] = '';, it is better to leave it blank, just like when loading CI.
-, $config['base_url'] - http:// .
, base href -:
<base href="http://www.mysitedomainname.com/" />
- , site_url(), base_url() , js, img src URL. : base_url() index_page, config.php.