This documentation is not using the current rendering mechanism and will be deleted by December 31st, 2020. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
The extension Start TYPO3 Responsive (start) is based on the responsive framework Foundation (zurb). If you like to adapt the design to your needs, Start TYPO3 Responsive +customer (startcustomer) extends Start with a user interface for configuring a lot of properties by mouse clicks.
The first both illustrations display two examples with +Customer.
The illustration on the bottom displays the foundation default design.