Custom CSS link issue

Hi, I've installed a local install of Drupal and OPIRNO. Everything seems to be working except when I make custom CSS changes through the Custom CSS panel on the config page it saves the CSS in the folder and I can see it on the server, but the site then tries to load the css with a link contain the C:\inetpub folder structure and not a web url link so the custom css file fails to load. What have I done wrong in the setup? http://......../C%3A%5Cinetpub%5Copigno%5Csites%5Cdefault%5Cfiles%5C4884b3b968c28b610f2610b8892b570857f3c7ab4609b_platon_override.css?oein2a