Happy 2014 is a responsive theme created by Katie Harron. It features mobile navigation for small screens, lazy loading of images, responsive images and photosets, responsive videos, a plethora of social icons, and much more. A current preview of the theme is available at http://happy2014theme.tumblr.com. I hope you enjoy it and/or find it useful if you're trying to build your own theme. The source code is available on Github.
This theme is free for personal use and can be modified with your own custom CSS. All I ask is that you keep the link back to my blog in the footer and do not claim the code as your own.