Edit: try searching under
app/assets/stylesheets
Here is an example
https://github.com/joliss/solitr/tree/master/app/assets/stylesheets
I'm not very good at rails application structure, but have you created a local copy or are you using bootstrap files hosted directly by github? You should understand this by checking one of your running html pages and looking at the source code, looking for something like
<link rel="stylesheet" href="http://twitter.github.com/bootstrap/1.3.0/bootstrap.min.css">
If this is a local page, your rails application should have some kind of directory where the files are stored - maybe there is a static folder or something like that? Try searching for files so that you can find.
(I use Django / Python for web projects, but I will borrow Rails a bit and see if I can find anything)
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