Accordion: card-header border bottom hidden by card-body.

Created by: MargotPiva

When an accordion element is open, the border bottom of the card-header element is hidden by the card-body element (in case of non-transparent background). See here the actual comportment : https://codepen.io/anon/pen/GzjNYL. This behavior is due to this :

https://github.com/twbs/bootstrap/blob/e65dccfc95c04aba3de66d9880ad1e6852b659f2/scss/_card.scss#L286

This addition is due to those issues : #27124 (closed), #27108 (closed). The bug reported here was the double border-bottom between the accordion elements when closed.

See the result when removing the rule over the margin-bottom : https://codepen.io/anon/pen/XOjNGz Unfortunately the double border-bottom is back but the behavior of the card-header of an open element seems correct with a border-bottom.