Suggestion: Use Hypermedia. Benefit: Your choice of URIs doesn't matter as much.
If providing sources in a visible fashion to your end-user, in the course of their normal use of your web application:
<a target="_blank" href="http://www.example.com/css/styles.css"
rel="sourcecode" title="The non-minified CSS source.">
Click here for CSS source code. </a>
<a target="_blank" href="http://www.example.com/scripts/buttons.js"
rel="sourcecode" title="The non-minified JavaScript source.">
Click here for JavaScript source code. </a>
If providing sources to developer users, outside course of their normal use of the web application, it might make sense to reference them in a non-visible section of the source:
<link rel="sourcecode" type="text/css"
href="http://www.example.com/css/styles.css"
title="The non-minified CSS source." />
<link rel="sourcecode" type="text/javascript"
href="http://www.example.com/scripts/buttons.js"
title="The non-minified JavaScript source." />
These links will only be available to developers who view the source of the HTML, or folks who have really tricked-out user-agents.
Along the same lines, you could put the non-minified CSS (but not JS) source as an alternate stylesheet.
Note: rel="sourcecode"
isn't a standard (I just made it up), but I'm pretty sure it doesn't violate spec; and along with the title
it helps to communicate the purpose of the link.