Unknown CSS

Hi,

When using Inspect Element within Google Chromes tools. I can usually hover over the path above the CSS to find the exact path of the stylesheet… many times I come across CSS which has the path of only the domain, why is this and how can I change this CSS?

I try to overwrite it in the main style.css but the mystery CSS never changes.

Here’s a screenshot to show the view.

Any help appreciated

Thanks
J