How to routes.MapPageRoute() to route non-existing path to a working path?

I'm in my 2nd day now and I still couldn't figure out how to make this work.  I'm using Web Application having both WebForm and Razor webpages, .NET framework 4.5.1.
In html script like <style type="text/css" rel="stylesheet" href="rCss/global1.css" />, it would sent out https://www.foo.com/rCss/global1.css.   But the physical filepath is ~/Webpages/Css/global1.css .
With the routing I used, routes.MapPageRoute("Css","rCss/{file}","~Webpage/css/{file}"); I still get a 404 not found error in web browser.

So, what did I do wrong?  Thanks...