Preview Not Working

When I go into the Settings on the WP Dashboard and click on the “Style” tab & then click on the Preview WP UI CSS3 Styles I get the following error:

[ Moderator note: for that output please use the code button and not blockquote. It formats better that way. ]

WP_Error::__set_state(array(
   'errors' =>
  array (
    'http_request_failed' =>
    array (
      0 => 'couldn\'t connect to host',
    ),
  ),
   'error_data' =>
  array (
  ),
))
Failed to load File. Double check URL or maybe the installation didn't go well?

It happens on every website I use it on.

Here are a couple of examples:

https://2supportu.biz
https://photoboothhireuk.com

https://www.ads-software.com/extend/plugins/wp-ui/