CMS Suite v3 comes with its own default design using Bootstrap by Twitter. Bootstrap is a Sleek, intuitive, and powerful front-end framework for faster and easier web development. All elements of your site design can be altered by modifying the bootstrap source files. See here to access docs on how to customize bootstrap: http://twitter.github.com/bootstrap/
However, If you are looking for a 3rd party theme/design that you can use with CMS Suite v3, Checkout the thousands of free and premium Bootstrap templates that are web-ready and mobile ready at the same time.