your site is not getting proxied thorugh CloudFlare ()
your site requests a CSS file which does not exist
For both things CloudFlare can not do anything.
I would recommend to activate CloudFlare for more then just DNS () and then clearing your Cache in WP Backend and regenerate.
Also you are using “siteground-optimizer” which is good, but actually somehow your WordPress Cache is not getting regenerated/flushed and therefore the HTML links to a non existing CSS file.
But just to clarify this: this is not related to CloudFlare.