Due to the complexity of the underlying code in Fabrik, and to ensure that your portfolio site looks and loads correctly across all different types of devices and screens (from mobile to tv and broadcast), we cannot grant full access to the CSS.
However if you know how to use the inspector in your browser and some basic HTML and CSS knowledge you can add overriding CSS in the Settings > Advanced > HTML Head Content area. This area is the HEAD section of the HTML document so make sure any CSS is wrapped in the appropriate style tags.