This.. is.. remarkably strange.
Just spent a good portion of maybe over an hour trying to wrap my head on this.
I have a project made with cshtml files. Using the Razor syntax.
The style is referenced the good old way
When I run it using IIS-Express, I have no problems whatsoever. It runs, renders and looks really nice.
THEN I deploy it on IIS (on Windows 8).
The problem was that it displays only the basic HTML, no script, no styling whatsoever.
So I try to open the CSS file on the browser, and nothing. Just nothing.
Make sure you check/enable Static Content.