Equivalent to plugins_url('css/file.css',__FILE__) for mu-plugins dir?

I’m looking for an equivalent mapping of the plugins_url( .. ) function for use within the context of the mu-plugins folder. My stylesheets are currently reporting back as 404 Not Found.

Current code (from non-mu-plugin dployment) is:
plugins_url('/css/my_plugin.css',__FILE__)

This is breaking in part I think becasue the Ubuntu server I am on has symlinks pointing from the “real” location (where apache looks for it) of
/var/libwordpress/wp-content/mu-plugins/.

The actual files are located in ~web-owner/wp-content/mu-plugins/.

What I see in the browser is a mash up:
subdomain.domain.ca/wp-content/home/web-owner/wp-content/mu-plugins/my_plugin/my_plugin.css
Which is obviously junk.

Thoughts? Anyone?
TIA
Erik