Have a look in the inspector at this site:
https://artglassandmetal.com/

The file at https://artglassandmetal.com/media/templates/site/j51_verona/css/vendor/joomla-custom-elements/joomla-alert.min.css?0.4.1, is importing another file at the top, using a relative link, check this screenshot:

https://i.imgur.com/fI8nWaO.png

This link resolves to https://artglassandmetal.com/media/templates/media/vendor/joomla-custom-elements/css/joomla-alert.css, which is an incorrect path.

So what's the fix?