You mean like in this fiddle? http://jsfiddle.net/EfEuw/3/
The bootstrap source url is //netdna.bootstrapcdn.com/bootstrap/3.0.3/css/bootstrap.min.css
so all you need to do is add it do external resources.
If you are using a fiddle, I would suggest just using the same sources that the examples use, because they are already hosted on the web.