The frontend UI that comes out of the box is intended to serve as an example and is not exhaustive. Some parts may or may not be completely responsive, and it does not necessarily contain every single feature of things that you can do with Broadleaf.
In our new demo coming in the next couple of weeks, it will be a much better starting point and designed to customize (e.g. based on Bootstrap, comes with some out of the box transferrable styles).
The Broadleaf forums are being retired as a readonly archive of questions. For active discussions and questions, check out the broadleaf-commerce tag on Stack Overflow
which is actively monitored by the Broadleaf team.