As CakePHP 3x has inbuilt responsive feature, I would like to know the element structures and class definitions.
I\'m indeed familiar with Twitter Bootstrapping ( done
CakePHP 3 uses the Zurb Foundation front-end framework 'out-of-the-box'. Which means that the classes you want to use will be listed in their documentation.
Specifically the page about the grids.
You can customise, remove or replace the provided default css if you want to. It is only provided so that you can 'hit the ground running' and so that new users are presented with a more organised front-end look when they first start using the framework.
If you'd like to review the history of this change, you can check the PR on Github.