This answer might not seem very useful right now, but tools which automatically generate xpath or css for an element pretty much never do a good job of creating a selector which is not brittle.
I strongly advise that you spend a day or two learning in depth either xpath, or css (Webdriver supports either, css selectors tend to be a bit quicker) as it is not complicated, and not rely on automatically generating selectors, they really cause a lot of problems and very very weak tests that break quickly.
For example, if we add in another div somewhere in the middle of the other 7 you already have before your element, the xpath you have there breaks entirely. Xpath in the right hands can be well written and quite robust.
Quick answer : btn is the class on your link. It looks like it's been decorated with the same class twice (smells wrong to me).. The css selector would be a.btn if the btn class is unique on all a tags like you said.