The .card-group class is similar to .card-deck, which creates an equal height and width grid of cards.
However, the .card-group class removes left and right margins between each card.
In this example we have added extra content to the first card, to make it taller. Notice how the other cards follow.
Note: The cards are displayed vertically on small screens (less than 576px), WITH top and bottom margin:
Some text inside the first card
Some more text to increase the height
Some more text to increase the height
Some more text to increase the height
Some text inside the second card
Some text inside the third card
Some text inside the fourth card