Javascript for css based on platform

[cushybaby]

I've tried using an "if" javascript code snippet to write a link to the proper css based on platform. However, it does not seem to write in the head, you just see the code and the CSS is not utilized. Any pointers?

The external js file is attached.

Thanks in advance.

[cushybaby]

The css, external js, and web files are all in the same directory. If you'd like, here it is online: