Card descriptions can be added a couple of different ways, depending on if you want them to appear only in the card or both card and topic.
For example:

The description in the card will wrap in accordance with the browser width.
Specify the metadata directly in the topic's yaml header.
meta:
- name: card-description
loccontent: Such a card description does not appear in the card topic, only the card.Wrap the card description in a style helper
{{#style "card-description"}}
Such a card description appears both in the card topic as well as the card.
{{/style}}Specify the callout in the metadata in the topic's yaml header.
meta:
- name: card-description-callout
loccontent: "Calling out callouts:"The callout is prepended to the card description in boldface, separated by a blank.
Only loccontent values will be localized.