An alternative to copying the css file, is creating a symbolic link from somewhere in your meteor project, to the css file in the node_modules folder. You can check this symbolic into git, and meteor will pick it up like a normal file.
Just hit the same issue, I need to import the css from a react control. How do you actually go about creating a symlink? Is that a file shortcut/pointer at the filesystem level or is it a line you add to one of the config files?
There is an issue open for this already: https://github.com/meteor/meteor/issues/6037, it looks like @benjamn has put this into a post-1.3 bucket and will come back to it after 1.3… Maybe we can all add our thoughts in the Github issue, seems like importing CSS for a native NPM package would be important for 1.3 imo.