The following PR
introduced an override of the Bootstrap styles for .card-deck, .card, etc. through shortcodes/cards-pane.scss. This style overrides is an undesirable breaking change.
My guess is that this problem was introduced way back via:
but that it wasn't as obviously manifested until cards-pane.scss got processed along with all other Bootstrap styles (as is done in #1009).
The card-related style changes should only be applied in the context of Docsy cards and card-decks.
@deining - do you agree?
Edit: this also happens for the .td-content .highlight Docsy style.