Changes to the `card` customization id

The card customization id in the previous major version was the main and only container element for components. Outside the card element, a new cardBox id was introduced that allows more fine-grained style customization.

As a note, if you are changing the background color of card, you will also need to also apply the same color on the footer id as well. The footer now gray by default, and it’s located outside card, but inside cardBox.

A footerItem id was also added for more targeted styling of items inside the footer.