A website shows as insecure despite loading over HTTPS

Symptoms

• A website with a valid certificate is not shown as secure

  PLESK_WARN: Your connection to this site is not fully secure

• The source code contains links to non-secure resources over plain HTTP

  CONFIG_TEXT: <link rel="stylesheet" type="text/css" href="http://www.example.com/css/style.css" />
  <script type="text/javascript" src="http://www.example.com/js/jquery.js"></script>

Cause

Even though the website loads over HTTPS, some of its content loads over plain HTTP, and therefore shown as not secure.

Resolution

To fix the issue, update the insecure URLs in the site's code to HTTPS connections, or remove them. A web developer can identify the affected resources.