References
https://robots.thoughtbot.com/how-to-make-a-chrome-extension
https://developer.chrome.com/extensions/getstarted
http://stackoverflow.com/questions/11553600/how-to-inject-css-using-content-script-file-in-chrome-extension
http://stackoverflow.com/questions/9721344/my-css-is-not-getting-injected-through-my-content-script